A/C Compressor Trips Breaker

[Jim Jones]

I have a 2 1/2 ton rheem A/C unit that will kick on, but trips the breaker after a few seconds of running. It ran all Summer w/o problem, but began doing this just as the cool weather hit. The unit is from 1993, so it is older.

[paul52446m]

I have a 2 1/2 ton rheem A/C unit that will kick on, but trips the breaker after a few seconds of running. It ran all Summer w/o problem, but began doing this just as the cool weather hit. The unit is from 1993, so it is older.

You need to check the starting amps and the running amps to see what is going on. Do you have a crank case heater? Is it working? Check all wiring for burned
wires or lose connection. Check relays for bad points . You also could have a bad start capacitor. Later Paul

[Jim Jones]

Update to A/C Compressor Trips Breaker

Beautiful sunny day today, so I unwrapped the ammeter that I received at Christmas and did some testing.

Incoming voltage at the unit was 252VAC. Is that high? This is a 208/230VAC 1PH system. The circuit breaker is a pair of 50 amps, with a plastic connecting bar to move them in unison.

I hooked the ammeter loop on the incoming black wire, and manually made the contactor. The unit started up, and the first amp reading was 120. With time, the ready slowly declined. The reading was 102 when the breaker tripped off. The elapsed time on my stopwatch was 22 seconds. [I did it earlier w/o the stopwatch, and the amp reading started at 125 and ended at 115]. That does seem high to me, so I think we have ruled out the breaker. Is this a high starting amp reading for this unit? Or, is it supposed to tail off more quickly than it is?

As always, any advice would be appreciatted.


More unit nameplate info:
TRANE model TTN048C100A1, MFG DATE 9/93.
RATINGS
COMPRESSOR: 20.4 RLA, 122 LRA
COOLING FAN: 1.9 RLA, 1/4 HP

[paul52446m]

Beautiful sunny day today, so I unwrapped the ammeter that I received at Christmas and did some testing.

Incoming voltage at the unit was 252VAC. Is that high? This is a 208/230VAC 1PH system. The circuit breaker is a pair of 50 amps, with a plastic connecting bar to move them in unison.

I hooked the ammeter loop on the incoming black wire, and manually made the contactor. The unit started up, and the first amp reading was 120. With time, the ready slowly declined. The reading was 102 when the breaker tripped off. The elapsed time on my stopwatch was 22 seconds. [I did it earlier w/o the stopwatch, and the amp reading started at 125 and ended at 115]. That does seem high to me, so I think we have ruled out the breaker. Is this a high starting amp reading for this unit? Or, is it supposed to tail off more quickly than it is?




More unit nameplate info:
TRANE model TTN048C100A1, MFG DATE 9/93.
RATINGS
COMPRESSOR: 20.4 RLA, 122 LRA
COOLING FAN: 1.9 RLA, 1/4 HP

A Rheem unit that age 2and 1/2 ton should not be fused more than 25 to 30 amps. It should run at about 10 amps per leg and start at 20 to 25 max. per leg . Check my last posting on go from there. If you haven't burned up the compressor yet, you will if you keep trying it like you are doing. Paul

[Jim Jones]

Additional Info

I don't understand why on Dec 12 you would recommend that I check starting and running amps, then on Feb 5 you say I'm going to burn up the unit for trying it twice to get the reading you yourself recommended. What gives?

ps: Didn't put it in the previous post, but the nameplate recommends 50amp fusing.

Update: Just realized the LRA stands for locked rotor amps. What I heard earlier is the cooling fan kicking in, not the compressor.

[paul52446m]

I don't understand why on Dec 12 you would recommend that I check starting and running amps, then on Feb 5 you say I'm going to burn up the unit for trying it twice to get the reading you yourself recommended. What gives?

ps: Didn't put it in the previous post, but the nameplate recommends 50amp fusing.

Update: Just realized the LRA stands for locked rotor amps. What I heard earlier is the cooling fan kicking in, not the compressor.

Sorry i didn't mean it the way it came out. What i am saying is if you try it and the amps go real hi turn it right off so you don't damage something. thats why i was telling you what the amps should be..
I just went back and read all the post we have made and now you have me confused. You said you have a Rheems 2 and 1/2 ton air con. then you
put this info from the tag
More unit nameplate info:
TRANE model TTN048C100A1, MFG DATE 9/93.
RATINGS
COMPRESSOR: 20.4 RLA, 122 LRA
COOLING FAN: 1.9 RLA, 1/4 HP
This info says it is a Trane unit and it is a 4 Ton unit
So can you tell me what this means?
So you are saying now that the compressor never did start?
How many capacitors are in the out side unit? You should have a pro check the compressor for shorted or burned out. He could also check you capacitor.
It still could be a bad capacitor. Paul

[Jim Jones]

3rd installment, after additional testing today:

All three capacitors check out OK (starting, running & fan). Used the needle deflection test on an old analog meter. However, the resistor that sits across the starting capacitor is visibly charred and reads zero ohms. Don't know what resistance it is supposed to be. Wiring schematic attached:



I then disconnected the cooling fan from the system, and did the bump test again. Confirmed that the compressor IS coming on, but it sounds as if it is struggling to run slowly, and is groaning with a hi/low tone. Only left it on ~4 seconds, the amp reading was once again up around 120.

As always, any advice would be appreciated.

[HayZee518]

the resistor is supposed to bleed out the charge when the unit is off. check your nameplate current. says "FL" LRA is locked rotor current. normally when a motor starts it draws 125% more than nameplate current then settles down to normal run current. in an a/c, lack of refrigeration oil will make the motor run hotter than normal with an increase in current. a crankcase heater not working will put a burden on the motor. broken valves in the compressor will affect the whole system. too much freon charge like not enough freon will over burden the system.
CSR1 is normally closed and is in series with CSR which is a relay. what it does is discharge the CS or start capacitor in line with the start winding of the compressor just for an instant. the R is the run winding. 1OL is the system overload switch. [thermal OL]

[Jim Jones]

So, my A/C repairman came out today to troubleshoot the unit. The problem was.... (drumroll, please....) .....was the starting relay. Hooray. Very relieved. Much better than having to replace the entire outside unit. He replaced the relay and one of the capacitors for $100 (just because they come together as a set). It was the capacitor that had the fried drain resistor, so good.
Then, we notice that the cooling fan motor bearins are squalling. I guess from sitting through one more cold wet winter. I'll need to track one of those down. Found the exact match online at GSISTORE, but for $265 ? That sounds pricey for a 1/4hp motor. Also, I've got to fix the 24V control wire that the dog destroyed, and clean the coil up.
Maybe it will then make it through one more season.

[HayZee518]

grainger or hvac site should be able to supply a blower motor.

[brettyg]

Sounds like you are above LRA (locked rotor anps) BAd unit

[paul52446m]

Sounds like you are above LRA (locked rotor anps) BAd unit

how can it be bad when they got it going. paul

[brettyg]

Grainger is very expensive,
Try to call a Johnstone or Dreisilker motor supply
Hope this helps,
Chicago Heating And Air Conditioning Repair Service