# Walk-in freezer magnetic door switch



## erics37 (May 7, 2009)

Okay here's a little thing I encountered today that I could use some advice on.

Customer at a semi-fancy restaurant in the area has a walk-in freezer and a walk-in refrigerator. In the morning when the vendors deliver stuff, they prop the freezer door open for quite a while (like 30 minutes to an hour) because there's a constant stream of people going in and out. This causes all sorts of issues for the refrigeration units and lines and all that, they've had to call the refrigeration company out a few times to get the system back to normal.

I know almost zilch about refrigeration stuff so I don't know what the best solution to that would be, but what the maintenance guy at the restaurant is wanting is for the refrigeration units to shut off when the doors are open, and then restart when they close back up. If we do indeed go this route (unless one of y'all has a better suggestion), then I have a couple of options:

Option 1: Intercept the main circuit supplying the unit and run it through a contactor, and keep the coil energized through a door contact switch. The problem here is that the door contacts I can readily get a hold of can't handle very much current. A little contactor only draws maybe .1 amps at the most probably, but even that might be over the door contact reed switch ability.

Option 2: Find something on the low voltage side and switch it through a door contact switch. The walk-in already has a low voltage thermostat, if I just run a Normally Closed door switch contact in series with that, it should work too. However, I don't know exactly what the low voltage controls will run through the switch contacts current-wise.

The other thing I'm still iffy on is the door switch itself. I'm looking at these (GRI 4460 series):










(Here's a link to the cut sheet: http://www.grisk.com/commercial/pdf/4460%20Series.pdf)

Our local supplier is a distributor for GRI so they can get 'em easily. My problem is that on the cut sheet, it describes "open loop" vs. "closed loop" ... I know what that means in a process control setting, but not in this particular context. I just want to know what state the switch contact will be in when the freezer door is shut. :blink: Maybe I'll just get the SPDT switch and figure it out myself.

So, if you managed to get all the way to this point, please give me some suggestions. Thanks!


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## stuiec (Sep 25, 2010)

erics37 said:


> Okay here's a little thing I encountered today that I could use some advice on.
> 
> 
> So, if you managed to get all the way to this point, please give me some suggestions. Thanks!


Forgive me if this is way out to lunch, I'm just learning about some of this stuff, but is this a situation where you could use a little isolation xfrmr to deal with the current, and go ahead and use an LV contact at the door?


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## nitro71 (Sep 17, 2009)

Only problem I see is now the unit will shut down when people mommentarily open the door to get things from the cooler. I would suggest a toggle switch to turn off the cooler when the door will be open for extended periods of time.


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## crazyboy (Nov 8, 2008)

I would switch the low voltage wiring. Perhaps add a timed relay, then you don't have to worry about the load on the contact, and it would only turn off the unit if the door was open for x amount of time.


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## erics37 (May 7, 2009)

stuiec said:


> Forgive me if this is way out to lunch, I'm just learning about some of this stuff, but is this a situation where you could use a little isolation xfrmr to deal with the current, and go ahead and use an LV contact at the door?


An isolation transformer? Those are used to electrically isolate circuits from each other to knock down stuff like noise, etc. That wouldn't do anything for me.

The bottom line is that the door switch contacts are only rated at like, 5 or 10 watts, maximum of 175 or 200 volts or something like that. I think they were intended for use as power-limited switching devices for security alarm systems and whatnot.


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## erics37 (May 7, 2009)

nitro71 said:


> Only problem I see is now the unit will shut down when people mommentarily open the door to get things from the cooler. I would suggest a toggle switch to turn off the cooler when the door will be open for extended periods of time.


Fortunately all the shelves and stuff are pretty far away from the door. You actually have to go inside to get stuff, so there wouldn't be much rapid door switching going on.

A toggle switch simply wouldn't ever get used.



crazyboy said:


> I would switch the low voltage wiring. Perhaps add a timed relay, then you don't have to worry about the load on the contact, and it would only turn off the unit if the door was open for x amount of time.


That's an interesting idea. So you're saying to run the timed relay coil circuit through the door contact... it would probably be a small enough load that it would be within the door switch capabilities. Hmm lemme doodle it up.


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## erics37 (May 7, 2009)

Okay the only trouble with the timing relay is that if I wire the door switch in series with the thermostat loop, then the delay would also act when the thermostat tells the unit to shut off. It wouldn't be a big deal, but I'd rather not have it do that if it can be avoided.

I haven't looked at the low voltage crap so I don't know if there any additional terminals available for me to add an additional control loop through.


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## nitro71 (Sep 17, 2009)

Put it on a photo cell so when someone turns on the lights it shuts down :thumbsup: 

Not really sure a photo cell works off light bulbs.:laughing:

You're on the right track with the door switch. Might not be a low volt control on the freezer though. You should be able to install a small transformer and relay if neccesary.


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## JSpark (Nov 25, 2011)

Hey the photo eye idea is brilliant they definitely work off of a lightbulb


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## JSpark (Nov 25, 2011)

Photo eye is good for about 1000 watts that would be no problem controlling a contractor


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## Edrick (Jun 6, 2010)

It seems to me if you have it shutdown for an extended period of time you could run into thawing? I don't know how fast those walk in freezers cool down with the door open. But just wanted to bring it up. Now obviously the whole freezer won't turn into a puddle in 30 minuites.


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## Frank Mc (Nov 7, 2010)

Hi Eric

I would install the roller door contact you suggested...but i would install a small plc AB 810 say 8 in 4 out approx $130 AUS.....Set it up that if the door if left open say more than 10 minutes (programmable) operate two of the outputs one to trip a flasher and the other to trip a beeper (alert the staff)....Also have a reset button which will silence only the beeper...The flasher would reset once the door is closed ...You would have 2 spare outputs which you could link to the refrigeration circuit.....

HTH
Frank
PS....Using the plc gives you some flexibility...


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## eutecticalloy (Dec 12, 2010)

crazyboy said:


> I would switch the low voltage wiring. Perhaps add a timed relay, then you don't have to worry about the load on the contact, and it would only turn off the unit if the door was open for x amount of time.


I concur or however you spell it. I used to work for a company that intercepted the evap coil fans and and solenoid for refrigeration systems. Most commonly I would see a timing relay on the doors. More than five minutes open and they close the solenoid and turn off the evap fans. If the system is controlled by a thermostat/solenoid system just use the solenoid to turn off the compressor


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## eutecticalloy (Dec 12, 2010)

nitro71 said:


> Put it on a photo cell so when someone turns on the lights it shuts down :thumbsup:
> 
> Not really sure a photo cell works off light bulbs.:laughing:
> 
> You're on the right track with the door switch. Might not be a low volt control on the freezer though. You should be able to install a small transformer and relay if neccesary.


And when a worker forgets to turn off the lights????


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## eutecticalloy (Dec 12, 2010)

Edrick said:


> It seems to me if you have it shutdown for an extended period of time you could run into thawing? I don't know how fast those walk in freezers cool down with the door open. But just wanted to bring it up. Now obviously the whole freezer won't turn into a puddle in 30 minuites.


running the refrigeration with the door open is going to freeze up the evap coil quickly and will make it way harder to bring the system back down.

Just eliminate the human error and throw a beacon light and buzzer with its own high temp thermostat in there. Too warm here's the alarm


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## eutecticalloy (Dec 12, 2010)

erics37 said:


> Okay the only trouble with the timing relay is that if I wire the door switch in series with the thermostat loop, then the delay would also act when the thermostat tells the unit to shut off. It wouldn't be a big deal, but I'd rather not have it do that if it can be avoided.
> 
> I haven't looked at the low voltage crap so I don't know if there any additional terminals available for me to add an additional control loop through.


NC contacts of the timing relay then when the thermostat closes as long as the door hasn't been left open for too long it will still call.


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## MechanicalDVR (Dec 29, 2007)

JSpark said:


> Hey the photo eye idea is brilliant they definitely work off of a lightbulb


 
No that idea isn't good at all, 99% of the time people leave the light on, for many reasons.


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## MechanicalDVR (Dec 29, 2007)

First of all the units should have plastic strip doors for loading/unloading. This is a very common problem all over. Secondly I have never seen any commerical walk in with anything but line voltage controls, never low voltage. Secondly, the evap fans could be on a door switch to stop blowing warm air over the coils and the evap t-stat will shut the compressor off.


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## BBQ (Nov 16, 2010)

I do lots of freezers, it is still hard to generalize as they can be set up many ways.

That said, you do not want to shut the evaporator fans down without shutting down the refrigeration as doing so can freeze up the evaporator coils.

All the supermarket freezers we do have door switch to shut down both the fans and the refrigeration. This is a money saving and employee comfort thing. In our case the switch is just a simple mag switch that controls an input of control system so the current is low. As DVR the mentioned they should have the plastic strips to keep the heat out when the door is open. In our case if the door switch is open for more than 45-60 minutes the control system generates a phone call to tell them to close the damn door.:jester:

Eric, I am going to assume you are dealing with a self contained unit?

I would get a RIB http://www.functionaldevices.com/building-automation/drycontact.php that has it's own low volt, low current control circuit the magnet could handle.

Use it to kill the fans and compressor in some way.

You could add a time delay relay to keep things from short cycling.

You could also add another time delay relay to trigger some sort of indicator if the door was open too long.


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## crazyboy (Nov 8, 2008)

erics37 said:


> Okay the only trouble with the timing relay is that if I wire the door switch in series with the thermostat loop, then the delay would also act when the thermostat tells the unit to shut off. It wouldn't be a big deal, but I'd rather not have it do that if it can be avoided.
> 
> I haven't looked at the low voltage crap so I don't know if there any additional terminals available for me to add an additional control loop through.


The way I'm imagining it, it wouldn't do that. Ill try to draw it out later and see.


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## bmart (Dec 28, 2011)

And what happens when the door is closed and the switch malfunctions and freezer does not turn on? I would try something different. Connect an audible alarm to the thermostat or independent from it when the temperature gets above 20F, it sounds an alarm. I never heard of this being a problem before. Why don't they educate their vendors and personnel?

bmart


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## erics37 (May 7, 2009)

MechanicalDVR said:


> First of all the units should have plastic strip doors for loading/unloading. This is a very common problem all over. Secondly I have never seen any commerical walk in with anything but line voltage controls, never low voltage. Secondly, the evap fans could be on a door switch to stop blowing warm air over the coils and the evap t-stat will shut the compressor off.


Actually looked at the place today. You're right, line voltage controls! I'll keep that in mind for future reference.

Looks like the plan is gonna be using the door switch to operate the RIB dry contact relay that BBQ suggested (turns out we had a few in the shop underneath a pile of crap!) which will in turn operate whatever controls get decided on. My final question is what do we want to kill when the door opens and the time delay passes? The solenoid, the fans in the freezer... Or should I just kill the whole thing?



bmart said:


> And what happens when the door is closed and the switch malfunctions and freezer does not turn on? I would try something different. Connect an audible alarm to the thermostat or independent from it when the temperature gets above 20F, it sounds an alarm. I never heard of this being a problem before. Why don't they educate their vendors and personnel?
> 
> bmart


The vendors don't care and the personnel no hablan ingles.


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## eutecticalloy (Dec 12, 2010)

erics37 said:


> Actually looked at the place today. You're right, line voltage controls! I'll keep that in mind for future reference.
> 
> Looks like the plan is gonna be using the door switch to operate the RIB dry contact relay that BBQ suggested (turns out we had a few in the shop underneath a pile of crap!) which will in turn operate whatever controls get decided on. My final question is what do we want to kill when the door opens and the time delay passes? The solenoid, the fans in the freezer... Or should I just kill the whole thing?
> 
> The vendors don't care and the personnel no hablan ingles.


Just the solenoid and fans. The solenoid closing will throw the compressor into as vaccum causing it to shut off.


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## crazyboy (Nov 8, 2008)

Found an error in my drawing already.


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## BBQ (Nov 16, 2010)

erics37 said:


> My final question is what do we want to kill when the door opens and the time delay passes? The solenoid, the fans in the freezer... Or should I just kill the whole thing?


If you have a solenoid available to kill I would kill that and the fans, as was noted closing the solenoid allows the compressor to 'pumpdown' and shut itself off. This is desirable.

You would not choose to kill it all if you can avoid it.


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## mgraw (Jan 14, 2011)

On a freezer I would put a switch on the door and break the t-stat circuit. If the door is open the unit shuts off. 
http://www.grainger.com/Grainger/DA...cm_sp=IO-_-IDP-_-RR_VTV70300505&cm_vc=IDPRRZ1


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## BBQ (Nov 16, 2010)

mgraw said:


> On a freezer I would put a switch on the door and break the t-stat circuit. If the door is open the unit shuts off.
> http://www.grainger.com/Grainger/DA...cm_sp=IO-_-IDP-_-RR_VTV70300505&cm_vc=IDPRRZ1


Breaking the T-stat will not kill the fans which is often what they want.


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## wildleg (Apr 12, 2009)

fire the employees and get some that have worked around freezers

install this:
http://www.pvcstrip.com/


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## mgraw (Jan 14, 2011)

BBQ said:


> Breaking the T-stat will not kill the fans which is often what they want.


 True but that is not what the OP stated as being the problem. If that is the problem, assuming this is a small freezer, the same switch could be used but the the circuit would need to be broken at the time clock.


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## Southeast Power (Jan 18, 2009)

BBQ said:


> You could add a time delay relay to keep things from short cycling.
> 
> You could also add another time delay relay to trigger some sort of indicator if the door was open too long.


The first thing I thought of was was that a simple switch would short cycle the equipment.


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## BBQ (Nov 16, 2010)

jrannis said:


> The first thing I thought of was was that a simple switch would short cycle the equipment.


We have a short time delay that ignores if the door is just open and closed and once that is triggered there is a longer delay after the door is shut. 

In our case it is just a matter of programming the time delays into the controller.


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## BBQ (Nov 16, 2010)

mgraw said:


> True but that is not what the OP stated as being the problem. If that is the problem, assuming this is a small freezer, the same switch could be used but the the circuit would need to be broken at the time clock.


If the door is open leaving the fans on is, well, stupid.


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## Southeast Power (Jan 18, 2009)

BBQ said:


> If the door is open leaving the fans on is, well, stupid.


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## BBQ (Nov 16, 2010)

jrannis said:


>


:lol:


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## mgraw (Jan 14, 2011)

BBQ said:


> If the door is open leaving the fans on is, well, stupid.


Stupid... maybe but very common. I really doubt a restaurant is going to spend thousands of dollars to put a controller on a small walk-in freezer. In your world of multi-million dollar supermarkets it is common. It is not common in small applications.
As far as short cycling if the door is opened the unit will began pumping down. If it is closed before the unit completes pumping down the unit will stop pumping down and continue to run. If the door is closed after the unit completes pumping down the valve will open and when the pressure in the lines increase to the proper level the unit will start running again.


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## randomkiller (Sep 28, 2007)

BBQ said:


> If you have a solenoid available to kill I would kill that and the fans, as was noted closing the solenoid allows the compressor to 'pumpdown' and shut itself off. This is desirable.
> 
> You would not choose to kill it all if you can avoid it.


 
Keep your work inside the box, killing the liquid line solenoid will shut off the compressor(s) and the coil getting warm will stop the fans (they work off coil temp). In most cases there is no wiring inbetween the box and the compressor, so shutting off both will get involved.


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## erics37 (May 7, 2009)

randomkiller said:


> Keep your work inside the box, killing the liquid line solenoid will shut off the compressor(s) and the coil getting warm will stop the fans (they work off coil temp). In most cases there is no wiring inbetween the box and the compressor, so shutting off both will get involved.


Okay so now you're saying just kill the solenoid.

This site is amazing. I can get tons of info on almost any topic but it all disagrees with each other so in the end I walk out with nothing but a headache :laughing:


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## mgraw (Jan 14, 2011)

What you need to do depends on what you are trying to accomplish. You stated leaving the door open was causing problems. What kind of problems? Are the employees shutting off the fans?


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## erics37 (May 7, 2009)

mgraw said:


> What you need to do depends on what you are trying to accomplish. You stated leaving the door open was causing problems. What kind of problems? Are the employees shutting off the fans?


As someone else stated, leaving the door open and the unit running will freeze up the coil in short order.

I'm gonna go with majority opinion and kill the solenoid and fans on, say, a 30 second delay.


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## Wirenuting (Sep 12, 2010)

The bad thing about killing the coil is that the unit will most likely trip on a HP cut out. It "should" reset after the pressure equalizes. It should then cycle back on.

If it was me I would break the HP switch. The unit will then stay off, equalize and then cycle back on after the door is closed.

That will cause less damage to the unit in the long run. But it is based on it being a sealed unit and not one of them modern scroll ones..

Why don't you head over to the ACTalk site and troll there... You will find the best answer.


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## mgraw (Jan 14, 2011)

Wirenuting said:


> The bad thing about killing the coil is that the unit will most likely trip on a HP cut out. It "should" reset after the pressure equalizes. It should then cycle back on.
> 
> If it was me I would break the HP switch. The unit will then stay off, equalize and then cycle back on after the door is closed.
> 
> ...


 You cannot be serious. You can do major damage breaking the high pressure cut out. The unit will not cut out on low pressure, as it would do cutting the solenoid, and would try to restart under high pressure.


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## Wirenuting (Sep 12, 2010)

mgraw said:


> You cannot be serious. You can do major damage breaking the high pressure cut out. The unit will not cut out on low pressure, as it would do cutting the solenoid, and would try to restart under high pressure.


If it wrote it, I must have been serious. 
Without arguing who will do the least damage, reread my last statement to him.
Head over to the ACtalk site and get advice from the guys who do this for a living. 


Anyone of us can "do things" with a refrigeration unit,, but at the end of the day we're still electricians. 

It never hurts to aim a question at the tradesman who might be able to give the best answer..


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## mgraw (Jan 14, 2011)

Wirenuting said:


> If it wrote it, I must have been serious.
> Without arguing who will do the least damage, reread my last statement to him.
> Head over to the ACtalk site and get advice from the guys who do this for a living.
> 
> ...


 It is obvious one of us has no clue what they are talking about. Since I know what I am talking about, it must be you. I am licensed HVAC and electrical, got my start doing refrigeration and have been doing it for 35 years.


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## Wirenuting (Sep 12, 2010)

mgraw said:


> It is obvious one of us has no clue what they are talking about. Since I know what I am talking about, it must be you. I am licensed HVAC and electrical, got my start doing refrigeration and have been doing it for 35 years.


.....


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## mgraw (Jan 14, 2011)

Wirenuting said:


> Well at least I didn't say you were clueless.
> If you can give him the right advice then do it. If all you want to do is point fingers then stick that finger were it belongs.
> And I'm sooooo impressed. 35 years of hacking 1 of 2 trades. I've only been doing stuff for about 15 minutes.


 I gave the OP advice. He chose to take others advice. That is his problem. I don't hack any trade. The company I worked for 35 years ago went into the electrical business because we were tired of dealing with electrical hacks.
Have a nice day


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## Wirenuting (Sep 12, 2010)

mgraw said:


> I gave the OP advice. He chose to take others advice. That is his problem. I don't hack any trade. The company I worked for 35 years ago went into the electrical business because we were tired of dealing with electrical hacks.
> Have a nice day


.....


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## MechanicalDVR (Dec 29, 2007)

Wirenuting said:


> The bad thing about killing the coil is that the unit will most likely trip on a HP cut out. It "should" reset after the pressure equalizes. It should then cycle back on.
> 
> If it was me I would break the HP switch. The unit will then stay off, equalize and then cycle back on after the door is closed.
> 
> ...


 
Wow you are way off, if you close the liquid line the unit will pump down and shut off on the operating pressure control , no way in hell will it open the HP switch or raise the hot gas pressure.


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## MechanicalDVR (Dec 29, 2007)

Wirenuting said:


> If it wrote it, I must have been serious.
> Without arguing who will do the least damage, reread my last statement to him.
> Head over to the ACtalk site and get advice from the guys who do this for a living.
> 
> ...


 
Do you know what a sight glass should look like with the unit running? Can you give us a brief description?


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## mgraw (Jan 14, 2011)

Wirenuting said:


> I'm glad to hear your company, with your assistance, is ridding the world of electrical hacks. That's very commendable.
> So let me get this strait. For the last 35 years you have worked for an electrical contractor. Since you have been doing this stuff for 35 years it makes it sound as if you had a few weeks as an AC guy when you first started out.
> 
> Who's advice the OP used is best determined by him. Right wrong or in the middle, he is the one standing on his job site and might be more clued in then you or I.
> ...


 Learn to read and don't give advice when you are ignorant to the subject.


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## Wirenuting (Sep 12, 2010)

MechanicalDVR said:


> Do you know what a sight glass should look like with the unit running? Can you give us a brief description?


You very well could be right about the HP cut out. I'm not and nor will I ever claim to be an AC person. That's a trade all in it's self. 
When I work on a chiller, absorber or what ever, it is only to help trouble shoot or replace parts. I do not have nor will I ever want to get my universal, it's not what I want. My boss wants us all to get them but I'm a hold out. I am not a believer in the concept of, if you have it you can do the work..

As for the sight glass, which type do you want me to tell you about?


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## Wirenuting (Sep 12, 2010)

mgraw said:


> Learn to read and don't give advice when you are ignorant to the subject.


.....


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## mgraw (Jan 14, 2011)

Wirenuting said:


> I like you,,, you must be ReWires little sister.


 LOL this from Roadhouse's protégé.


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## Wirenuting (Sep 12, 2010)

HP cut-outs stop the compressor if the pressure on the high-pressure side becomes excessive. This control appears in the wiring diagram as a NC control that opens on a rise in pressure. The manufacturer may determine the upper limit of operation for a particular piece of equipment and furnish a high-pressure cut-out control to ensure that the equipment does not operate above these limits.
A compressor is known as a positive displacement device. When it has a cylinder full of vapor, it is going to pump out that vapor or stall. If a condenser fan motor on an air-cooled piece of equipment burns out and the compressor continues to operate, very high pressures will occur.
* the high pressure control is one method of ensuring safety for the equipment and the surroundings. Some compressors are strong enough to burst a pipe or a container. The overload device in the compressor offers some protection in this event, but it is really a secondary device because it is not directly responding to the pressures. The motor overload device may also be a little slow to respond.* 
Page 229

<sorry, I don't know how to read, I only know how to copy letters>


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## Wirenuting (Sep 12, 2010)

mgraw said:


> LOL this from Roadhouse's protégé.


LoL,,, that was a good one.


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## Wirenuting (Sep 12, 2010)

Hey Mgraw,
I can respect you for your knowledge and I'm sure that some day I might even as follow advice from you.


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## mgraw (Jan 14, 2011)

Wirenuting said:


> Hey Mgraw,
> Can we call it even and stop trying to insult each other?
> We both know we can't win.
> I can respect you for your knowledge and I'm sure that some day I might even as follow advice from you.


 EVEN, you give bad advice and when you are called on it you resort to personal attacks. I am still laughing at you. You made my day.


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## Wirenuting (Sep 12, 2010)

mgraw said:


> EVEN, you give bad advice and when you are called on it you resort to personal attacks. I am still laughing at you. You made my day.


.....


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## erics37 (May 7, 2009)

Gentlemen, thank you for the advice on this topic. It is one shrouded in mystery to me, and all of you have contributed to the unveiling of this mist. But would you two shut the f**k up? Your chest-puffing is getting old.


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## Wirenuting (Sep 12, 2010)

erics37 said:


> Gentlemen, thank you for the advice on this topic. It is one shrouded in mystery to me, and all of you have contributed to the unveiling of this mist. But would you two shut the f**k up? Your chest-puffing is getting old.


Ok, sorry eric37 for derailing the thread.


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## erics37 (May 7, 2009)

Wirenuting said:


> Ok, sorry eric37 for derailing the thread.


That looks like a fine book you posted though. Is there any particular book out there that is considered the "bible" of refrigeration or AC equipment?


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## Wirenuting (Sep 12, 2010)

erics37 said:


> That looks like a fine book you posted though. Is there any particular book out there that is considered the "bible" of refrigeration or AC equipment?


I only have a couple of books. That one is good for the basics and this one is from Carrier. Both are about 7 years old or so.
I have seen some of the service manuals that the manufacture reps carry, they are the ones that really would be nice to have.
But IMO, if all you do is minimal AC repairs, these two might be worth getting. 
This servicing procedure book even walk you thru identifying compressor start/run/common leads with your meter.
Both have service call problems and common answers. 
I think I got them thru the construction book store out of FL.
They are pretty good rookie books, that's why I have them.


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## erics37 (May 7, 2009)

Hmm, right on. I'll check Powell's Technical Books next time I'm in Portland.

Looks like Refrigeration & Air Conditioning Technology has a 4th edition out.

Correction, it's up to 6th edition!


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## MechanicalDVR (Dec 29, 2007)

erics37 said:


> That looks like a fine book you posted though. Is there any particular book out there that is considered the "bible" of refrigeration or AC equipment?


 
YES the absolute bible is the RSES (refrig. service engineers society) SAM manual (service and applications manual) but I believe you need to be a member to buy it and it's over $200. 

The one my old local uses in the classroom is Modern Refrigeration and Air Conditioning @$30 and Grainger used to carry it, not sure if they still do.


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## mgraw (Jan 14, 2011)

I agree the Modern Refrigeration and Air Conditioning book is the second best book out there.


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## erics37 (May 7, 2009)

Okay I went to the library today and checked out all 2 of the refrigeration books they had there. They are both pretty dated, but since all I really wanted was a survey-level overview of the topic, I figured they would be adequate.

One book is "The Air Conditioning/Refrigeration Toolbox Manual" by David Tenenbaum, copyright and publish date are 1990. It's mainly a basic reference guide rattling off theory of the refrigeration cycle, different types of systems, system components, etc. It's quite helpful to me so far in getting the basic terminology and whatnot down, and seeing how refrigeration systems work.

The other book is "Refrigeration: Home and Commercial (4th Edition)" by Edwin P. Anderson and Revised by Rex Miller. I haven't gotten into this one yet, but it looks a lot more in-depth and detailed. It has a few chapters on applications and controls too, so it may help.

Anyway, from the Toolbox Manual that I'm partway through, I have determined that closing the liquid refrigerant solenoid valve will initiate a "pumpdown cycle," which allows the compressor to pump all the liquid into the condenser or receiver, where it will sit until the next on cycle. Once it has sucked enough fluid through then the compressor's low pressure cutoff will engage and shut off the motor.

Am I reasonably correct in this analysis? If so, my question is how long would a pumpdown cycle last? Is it a matter of seconds? Minutes? Obviously it depends on the size of the system.... which I have no idea. The walk-in freezer is 10 x 8 x 6 or so, roughly 500 cubic feet, and is around roughly 0 degrees fahrenheit. If you sized a system for that, then how long would the cycle take?


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## MechanicalDVR (Dec 29, 2007)

erics37 said:


> Okay I went to the library today and checked out all 2 of the refrigeration books they had there. They are both pretty dated, but since all I really wanted was a survey-level overview of the topic, I figured they would be adequate.
> 
> One book is "The Air Conditioning/Refrigeration Toolbox Manual" by David Tenenbaum, copyright and publish date are 1990. It's mainly a basic reference guide rattling off theory of the refrigeration cycle, different types of systems, system components, etc. It's quite helpful to me so far in getting the basic terminology and whatnot down, and seeing how refrigeration systems work.
> 
> ...


 
As long as the liquid line solenoid is closed it will stay pumped down. Depending on what refrigerant is used and the setting on the low pressure control, when the system goes into pump down, the compressor may shut off and cycle once more shortly after and then stay off.

And you aren't pumping down liquid. The compressor pumps high pressure gas into the condenser were it condenses into liquid. The reciever and liquid line are the only two places you have liquid. Once the liquid enters the expansion device it expands into a low pressure low temp gas as it enters the evaporator, where it picks up the heat and becomes a saturated vapor that is sucked back to the compressor.


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