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Hi, I have a carrier 38ck060310 outdoor AC unit that is tripping the external 50amp breaker. I disconnected the compressor from the contactor and reset the breaker. The fan ran fine. Is there any additional tests that I can do to confirm that I have a dead compressor? Thanks Denis
Yes,Remove the wires of the compressor. Make notes on where you took them, then measure the resistance of the terminals against the body of the comressor. Set it to measure low resistance. You should not have anyt reading at all. If you do, that means the windings of the compressor is already grounded that is why the breaker is tripping.This would confirm that you have a bad comressor.
Hi Francis,I checked the resistance of the three power leads to the metal work of the unit (I assume that the compressor itself would be grounded to the metal work). That showed no connection. So I don't think that the motor coils are shorted to ground.When I checked the resistance between phases it was about 35 ohm. But between one phase and the connection to the starting cap, one phase was about 5 ohm and the other was much higher.Does that make any sense?
You do have a single phase comressor or three phase?I am surprised you did not have grounded winding. Did you tried it to a bare metal or a bare copper tube from the compressor? You may need to file it a bit in order to really get the metal body. Just to be sure.
It's a single phase motor, connected to 220V, so two AC phases.But there's a third connection to a starting cap.I'll recheck the measurements to ground again tonight.Can I leave this case open and get back to you later?
Sure.I will log off anyway too.If it is single phase, then there would be a running capacitor. The resistance between the three terminals would be different then.We could label them C, for common, hooked up to one line of 220 then one would be the running, R, this would have the smallest resistance against C, and is hooked to one of the terminal of the capacitor and also it is connected to the other line of the 220. Then the last terminal should be S, for starting. This should have a bigger reading with respect to C and is connected to the other terminal of the running capacitor. The biggest resistance would be R and S which would be near the sum of the resistance of R and C and S and C.So if C and R is 5 ohms, then let say C and S is 24 ohms, Then R and S would be near 29 ohms.
Hi Francis. I made some measurements on the compressor last night. There are three wires, yellow, black and blue. Blue connects directly to the cap. Black and yellow connect to the contactor.All three are very high impedance to ground. I scraped the housing of the compressor to get a good contact. I used a regular multimeter. Do I need a megaohm meter for this?Then I measured the resistance between wires, as follows:yellow-blue: 35 ohmblack-blue: 7.8 ohmblack -yellow: 27.5 ohmBlue connects only to the cap, so I'll call that 'starting'. The other two I'm not as sure about, but I'll allocate them as follows:R = yellowC = blackS = blueWhich means:C-R = 27.5 ohmC-S = 7.8 ohmR-S = 35 ohmDoes this make sense?Denis
Hello Denis,Looks like you have done your homework. Very good. But the readings are inconsistent on how they are connected.C-R should be the smallest reading.C-S should be the medium reading and S-R should have the biggest reading which you have right now.There is another wire from the contactor that goes to the capacitor. Which wire is this and where does it connects to the contatctor? The yellow or the black?
Hi Francis,I took a look at the cap wiring. The yellow wire connects to the cap.The cap has three terminals. The center terminal is marked 'C' and is connected with a yellow wire to the compressor. Another terminal is marked 'FAN' and seems to connect to the fan. The third terminal is connected with a blue wire to the compressor.Denis
Ok.So the yellow wire goes to the C of the capacitor and also to the contactor. That would be our running terminal.So R-C should be the lowest resistance and yet your reading is 27 ohms which is bigger than C-S which is 7.8 ohms.You can try interchanging R and S and try it,If the comressor would run, then it might run in the reverse, discharge pipe would cool and suction pipe would heat up then you have a bad comressor.If the breaker would trip again, then you have a bad winding( Compressor).If the unit would run and cool down, then you have the wiring corrected.
The S wire (blue) has a different termination (spade) than the other two, so it definitely isn't misconnected.
Ok..So you have defenitely a bad winding based from the readings that you got.C-R should really be the smallest reading.
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