How to wire a fridge compressor?

Thread Starter

Tekat

Joined Mar 25, 2021
6
I removed a compressor from a small freezer. I need to be able to sort the wiring out now. There is an earth(yellow/green wire) attached to the body of the compressor which was attached to the casing of the freezer.

Then there's a wire connected to the thermal cut-off switch(white wire) and a blue(live I assume) wire attached to the power on the compressor.

https://i.ibb.co/0fv1bvt/PXL-20210325-150533285.jpg

Then there a plastic box where the white and blue wires go into, I think there are 2 fuses in this box but they may be other components, maybe this is a form of relay. There are 2 earth (green/yellow) in here that again were attached to the freezer casing, you can see how the other wires go.

https://i.ibb.co/txkmLL6/PXL-20210325-150624247.jpg

How can I set this up so I just plug the compressor in and it works, what do I do with the loose earth's, can I get rid of the wiring in the box?
 

Tonyr1084

Joined Sep 24, 2015
6,269
Welcome to AAC.

I can't tell you how to wire it - I've never done that. But I will sound a warning about compressed air. Unless you have a way of shutting the compressor off at a specific air pressure, you could end up with a dangerous situation where a tank could explode. More likely would be a burst air line, but you DO have to be careful.
 
Your "Two fuses", I think are just crimp connectors.

Usually a compressor is capacitor start and there is an external cylinder mounted somewhere with 2 wires.

I can't tell what I'm looking at. I do see the thermal.
 

Rich2

Joined Mar 3, 2014
190
That's a low starting torque compressor (no capacitor) like on all capillary domestic systems, it won't start up under load ie with the discharge at high pressure. On a fridge or freezer the in/out pressure always equals out after 2 minutes so it's not a problem. The bi-metallic overload will just pop after about 4 seconds if it can't start.. It resets in 2 minutes.
 

Thread Starter

Tekat

Joined Mar 25, 2021
6
That's a low starting torque compressor (no capacitor) like on all capillary domestic systems, it won't start up under load ie with the discharge at high pressure. On a fridge or freezer the in/out pressure always equals out after 2 minutes so it's not a problem. The bi-metallic overload will just pop after about 4 seconds if it can't start.. It resets in 2 minutes.
I can't say I understood that, I connected the brown and white cables and the 2 earth's together, it is starting but I've only run it for like 20secs your saying it will cut off?
 

Tonyr1084

Joined Sep 24, 2015
6,269
What Rich2 is saying is that the compressor can start when there is no back pressure. With back pressure the compressor motor isn't strong enough to start against an already pressurized system. In a closed loop like a refrigerator freon is pumped from one side to the other. The change in pressure produces heat, which is exhausted outside the refrigerator. Then the vacuum that is created on the other side, the drop in pressure chills the freon. Having blown the heat away the freon can get cold enough to freeze water and other things.

Because that's a closed loop, when the fridge is running the high pressure side, which started out as a static zero pressure, gets high while the other side, which started out as a static zero pressure drops to a vacuum. When the compressor turns off the pressure on both sides equalizes within minutes. Thus, the compressor has no load to fight when it starts up. However, if while the compressor is running and you have a power interruption, when power returns (if the pressure inside hasn't equalized) the compressor motor will stall and the overload will kick out. After a few minutes the overload will kick back in. If the compressor can start then the refrigeration process begins again.

If you use the compressor to charge an air tank then the tank will probably be close to ambient pressure (14 PSI depending on altitude) and the compressor can start. But if there's pressure in the tank - just guessing, but assume 25 PSI - that might be too much pressure for the compressor to start. It may stall and the overload will kick out.
 

MisterBill2

Joined Jan 23, 2018
9,294
Sealed unit compressors almost all have three terminals because there is a starter winding as well as the run winding. The start winding is only powered for a short time, while the run winding stays powered to run the compressor. So there is always a starter relay required. There is also, usually, an overload/over temperature witch to avoid burning out the motor. That switch is in series with the line connection so that it will switch off all of the power.
So if the TS is lucky, they have that starter relay as well. The green/yellow wires are all the safety grounding connection and not for running the motor. The other two wires are the power connections to run the motor.
I have read all of the comments and while some are correct, some are off the question.
 

Thread Starter

Tekat

Joined Mar 25, 2021
6
My goal was to use this compressor as a vacuum pump to vacuum my car's AC system. I've been told many times this isn't possible. From, cables that will collapse on themselves to not enough sucking power to the motor will overheat and burn out. But so far so good.

I did notice as you said that when I switch on the compressor at the wall it sometimes doesn't start but sometimes does, this must be to do with the pressure differences as you said.

There's no loss to me if it doesn't work as there is no monetary cost involved I just hope there nothing dangerous that can happen.
 

Tonyr1084

Joined Sep 24, 2015
6,269
Pulling a vacuum is similar to pumping pressure into a tank. The difference is you don't have a tank. Still, if the pump is on an evacuated line and you try to start it - the motor might not start. Again, it's the pressure difference.

As for pulling a vacuum on an AC unit - that requires a licensed technician with a system for capturing the old refrigerant. Unless you have the knowledge and the right tools for the job - it's best left to a professional. I realize you're trying to save a buck or two. But that's about all I can give you.

Blue and White are your Motor Run. Green/Yellow is ground. There is no third wire to be concerned with to run the motor.
There is always a starter relay required. So if the TS is lucky, they have that starter relay as well. The other two wires are the power connections to run the motor.
I have read all of the comments and while some are correct, some are off the question.
Did you look at the photographs? Shows only two wires going to the compressor. Blue goes to the motor, White goes to the thermal overload switch. From the OL switch to the motor. No third wires or relays involved.

Brown and White are the switched lines. Put a switch across the brown and white wire and you have your compressor pump.

1616774555656.png
 
Last edited:

MisterBill2

Joined Jan 23, 2018
9,294
Just because it does not show in the photo does not mean it is not there. OR the photo is after it was removed. The picture is not even looking at the right place or in the right direction.

Now consider that the only reason a person would be pulling a vacuum on an automotive AC system is to get the AIR out so that freon can be added. So the TS will not be pumping the freon out, but air. A very reasonable diagnostic process is to pull a vacuum and then connect a vacuum gage and see if air leaks back in. NONE of that testing involves anything except AIR. So there is no need for a license to do that, unless one lives in a police state.
And for a licensed tech to show up is $100, if all they do is say hello. So the chasing of leaks when the freon is gone is best done by somebody with time and determination. A bit of understanding is also useful.
 

Tonyr1084

Joined Sep 24, 2015
6,269
Well, the photo also doesn't show a Giraffe. But there must be one of those too. Right?

Tekat check with your local ordinances and find out if you can do as you want to. That way you don't go to jail in a police state.

If your AC leaks then it needs proper servicing. Replacing O-Rings at every joint is a start. But then you could be chasing a leak for the next six months. But if there's ANY freon in there at all - then you're probably breaking the environmental law. Not all people think it's a good idea to just run willy-nilly fixing things. Sure, if you can handle the job - fine. If you can do it environmentally safe - fine. If you have the equipment - fine. If not - - - .

Getting the air out - yeah, I understand that. And moisture too. But just because you're at zero PSI doesn't mean there's no gas in the pipes. And if "one" thinks it's OK to go ahead and blow that off - shame on that "one".
 
The big problem nowis the contamination of oils. R12 and R134a oils are not compatable.

https://www.hagerty.com/media/maint...oning-dos-and-donts-refrigerants-and-the-law/

Back in the R12 days and before the EPA, I used an old automotive compressor to pump down systems. Before I had my small appliance, automotive EPA license, I did an R12 AC install from a box of parts into a vehicle. Every 7 years, 2 hoses had to be replaced.

Before I had my EPA license, the evaporator in an R12 vehicle died and, it was dx'ed by a professional. he said you don;t want to pay for 14 hours of labor to fix it. I replaced the evaporator, pumped it down and did a leak-up test before returning it to the mechanic to charge.

I worked with vacuum, high vacuum and UHV systems. i.e. systems that could get to 1e-9 Torr. Those systems used an ion pump. A simple fingerprint would kill the ultimate vacuum. So, not even a fingerprint when I installed the R12 system. The O-rings got lubricated with refrigerant oil. The aluminum piping corrodes with fingerprint oils.

I had access to an electronic leak detector which was for R12 systems. When we upgraded the thermal detector at work, It was given to me. Matheson won't talk to me about the detector unless I was a business.
 

Thread Starter

Tekat

Joined Mar 25, 2021
6
Well, the photo also doesn't show a Giraffe. But there must be one of those too. Right?

Tekat check with your local ordinances and find out if you can do as you want to. That way you don't go to jail in a police state.

If your AC leaks then it needs proper servicing. Replacing O-Rings at every joint is a start. But then you could be chasing a leak for the next six months. But if there's ANY freon in there at all - then you're probably breaking the environmental law. Not all people think it's a good idea to just run willy-nilly fixing things. Sure, if you can handle the job - fine. If you can do it environmentally safe - fine. If you have the equipment - fine. If not - - - .

Getting the air out - yeah, I understand that. And moisture too. But just because you're at zero PSI doesn't mean there's no gas in the pipes. And if "one" thinks it's OK to go ahead and blow that off - shame on that "one".
I understand about the environmental regulations, also that zero PSI doesn't mean there's no gas and that you need certification to evacuate these gases as they contain chlorine.

It's a bit of a head twister as I'm broke atm and really need cold air in the car. Personally I doubt the fridge compressor will create a decent or any vacuum but if it does at least I'll be able to tell if it's leaking and how fast it's leaking. If I found out it had a bad leak then I'd have no choice to either change the o rings or get a garage to do it which I can't afford atm. I have the manifold/gauges kit so I can test for leaking ok.

Overall I have time on my hands and this is kind of a messing about project with the possibility that it may just work. I'm surprised the compressor is working at all but it is.
 

MisterBill2

Joined Jan 23, 2018
9,294
OK, T-1084. It happens that I have had quite a bit of experience dealing with assorted sealed unit compressors and I know where they are installed on a compressor and what they look like and how they work. And if it is a mains powered compressor and not some very recent electronic controlled motor, then it is an induction motor with a starter relay, that is almost always mounted right at the compressor. And what that relay does is disconnect the starting winding after the motor is spinning fast enough.
 
Personally I doubt the fridge compressor will create a decent or any vacuum
The fridge compressor should be fine UNLESS the oils are incompatible. That's not worth the hassle.

You can flush the compressor and change to a universal oil.

You should be able to pump down to -30, close off the pump and wait 3-4 hours. The longer, the better.

No one is going to use an RGA (residual gas analyzer) for AC systems. You can tell if the water is gone etc, heating the lines releases the water. If the guage hovers around 100um, it is usually not a leak. It's water.
 

Tonyr1084

Joined Sep 24, 2015
6,269
almost always
You keep saying that. Almost always leaves room for a two wire system. Unless I see a picture with a third wire (not the ground) - I'm going with a two wire system. They may "Almost Never" be two wire systems, but almost never leaves room that one could exist.

I worked with a woman who shouted at me "I HAVE 20 YEARS EXPERIENCE!" OK. But at the time I had 37 years. PLUS drafting training and I knew how to read AND DRAW blueprints. She insisted the customer would reject certain solder joints. I've worked with IPC (610) since its inception. I also know the Purchase Order would have to specify if they wanted something beyond IPC for a particular solder joint. This woman had 20 years. OK. But she was not as competent as she thought she was. Her QE (Quality Engineer) had been a QE for 3 years. Prior to that his experience was 5 years as an inspector. No formal training, not even some college related background training in blueprints.

When you tell me you have bocou experience - that's fine. But it's not the "Be All - End All" on the subject. The TS has stated his compressor is working fine. With just two wires. So I must draw the conclusion that it's a two wire system. Rare as it may be - it's a two wire system. Or so I believe it to be. With refrigeration - I have little experience beyond an old Ford Granada with a leaky AC. I bow to your greater experience. But I balk at the demand that it MUST be a three wire system. Maybe it is. Internally. IDK! No, really - I DON'T KNOW. But to get it up and running, the TS has wired the two wires as has been told him - and it's working.
I'm surprised the compressor is working at all but it is.
 

MisterBill2

Joined Jan 23, 2018
9,294
Tony, I suggest that you try and run a sealed unit refrigeration compressor using any combination of two pins only. You will find that it does not run. It will hum and get quite warm and eventually get hot, but it will not run. The reason for "almost always" is that there may be such a thing as a synchronous compressor motor or even a shaded pole motor, which would not be very efficient but it might not need a starter relay. So Always and never do not allow for exceptions, which may possibly be, but very seldom are.
And the fact that compressor relays do come in some strange looking packages means that some oof them do not look at all like the others.
AND, I have seen a compressor with a pin broken off, so that only two pins remained. It could be started by means of a momentary connection to the broken off pin stub by means of insulated pliers, and it was used by an old refrigeration mechanic to win a bet. I was quite impresed by how sneaky that was.
 
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