How to wire a fridge compressor?

Rich2

Joined Mar 3, 2014
254
Single phase refrigeration compressors always have 3 connections - CSR (common, start, run) the first photo shows the compressor has a current relay plugged onto it so you can't see the start pin. Other relays are potential relay and PTC relay. Never centrifugal relay in refrigeration (might have been 50 years ago )

Using a compressor as a vac pump will work but it won't pull down to -30psi like a vac pump will. An R22/R404a compressor or similar will pull down better than a R134a compressor because they are more heavy duty with higher head pressures on those refrigerants.

Edit: looking at the 1st photo again it might be a PTC relay.
 

MisterBill2

Joined Jan 23, 2018
18,167
Thanks, R2, for the comment. The fact that something is not seen does not mean that it is not there. Especially in a photo that doe not even show the item sought.
 

Tonyr1084

Joined Sep 24, 2015
7,852
Well scuse me. So it has an internal unseen wire. So how does this change the fact that the TS has his running with just two wires going to it? Picture or not - what's inside is something the TS can not (probably can't) get to.
 

Tonyr1084

Joined Sep 24, 2015
7,852
My 3/4 HP swamp cooler fan motor has only two wires (120VAC). It's all I can connect to. Well, that or for 240VAC, but I don't have that there. Internally there's a centrifugal switch that changes over from the start phase to the run phase. If I were to ask how to wire it would you tell me I need to connect three wires?
 

Thread Starter

Tekat

Joined Mar 25, 2021
6
Well scuse me. So it has an internal unseen wire. So how does this change the fact that the TS has his running with just two wires going to it? Picture or not - what's inside is something the TS can not (probably can't) get to.
Ok, to remove the bolts holding the compressor in at the back left side I removed what I'm sure where 2 wire connectors to the thermal cut off switch, you can see in the photo there is one wire connected but you can also see that there is an empty connection slot copper(or brass). I'm so sure I removed 2 connectors here thinking I would just reconnect them when I got the compressor removed and inside. By the time I got inside I could only see one wire, it really played tricks with my head and I looked everywhere for another wire but it appears there is only one wire with connection that plugs into the TCS.

Is there anyway of explaining this, maybe I did only remove one wire but I remember at the time I was sure it was two.

If it was two this could be your missing wire.
 

MisterBill2

Joined Jan 23, 2018
18,167
The only similarity between a swamp cooler motor and the compressor is the type of motor, being they are both induction motors. A sealed unit induction motor MUST use a relay to disconnect the start winding because a centrifugal switch in an oil bath will have problems. That switch is integral to the structure of the motor and when such a motor is removed from an assembly of some kind it usually comes with the motor. Starter relays are removed from the compressor fairly often by unknowing people, although some may correctly leave them in place. so the two situations are quite different.
On some compressors the starter relay actually plugs directly onto the three pins that come from the motor, and in those instances only two power connections will be seen. It might be that this is the setup on the compressor we see in the photo. But since all sealed unit compressors that have induction motors also have three terminals on the compressor body, at that point there must be three connections there.
AND, since we get the report that the compressor starts and runs, it must be that all three are connected.
 
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MisterBill2

Joined Jan 23, 2018
18,167
For de-gassing casting resins the vacuum should be adequate. But I suggest checking for oil mist prior to using it for the bubble removing, because refrigeration compressors do run submerged in oil.
There should not be any mist in the suction line, but there will be a bit in the discharge line. Just o you are aware in advance.
 

MisterBill2

Joined Jan 23, 2018
18,167
That is commonly called a starting relay. Without that the compressor will not start when the mains power is applied. This means that if you want to operate the compressor that item, or a replacement, MUST be connected. And the power needs to be connected to the two crew terminals, L and N.
Many of the starting relays are operated by the current drawn by the run winding of the motor, while some monitor the voltage, not sure just which voltage, and disconnect the starting winding when the voltage rises. I am not exactly clear on how that works, while the current operated relay operation is very obvious.
 
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