Bryant central A/C not working

My Bryant central A/C isn't working when I turned it on for the first time this summer. I did some trouble-shooting. It is getting power (3-phase 208 V). It's also getting 24VAC from the thermostat.

I can manually push in the contactor and it starts running (fans and, I believe the compressor). One of the refrigerant lines near the compressor gets hot.

I'm finding two reasons why the 24VAC isn't getting to the contactor:

1. The low-pressure switch is open. (The high-pressure switch is closed.)

2. This model has a CLO (compressor lock out). It has a small relay that becomes energized when the thermostat is turned on and this disconnects the 24VAC to the contactor.

Do I have two problems here or is one related to the other? Any help on where I should go from here? Thanks.

 

Does the large refrigerant line get cold?

 

Here's how the CLO works:

It monitors the amperage draw of the compressor. The 24 volt input [thermostat calls for cooling] signals the CLO to start to monitor. If the compressor stops running while the CLO still sees the 24 volt input, it's contacts switch and lock out the compressor by interrupting the circuit to the compressor contactor. Resetting the stat or power resets the CLO.

So what could make the compressor stop running?

a safety switch opens
the compressor internal protector opens

When you say the LP switch is open, how did you test it? If the compressor will run and produce cooling maybe you have a faulty switch. If you temporarily bypass the LP switch and start the unit, will it run? Let it run a couple minutes and see if it starts to produce cooling. Is there any correlation between a cool morning, the a/c running, and the lockouts? I've had to put LP switch bypass timers on units with CLO's to keep them from locking out on a cool morning.

 

No, it does not get cold.

 

Thanks for the detailed reply. It was very helpful.

I tested the LP switch with a continuity tester.

I bypassed the LP switch as you suggested and the contactor stays energized and the fans start up. I then waited a few minutes and the large refrigerant line does not get cold. So, that would seem to indicate that the CLO and the LP switch are both working and the problem is low refrigerant or there's a leak somewhere. Is that correct? Is there any additional troubleshooting I can do? Can I recharge it myself or do I need to call a professional?

 

OK, so the comp is not running, as "DJ" stated you can try to bypass the L/P switch and see if it runs. You may be low on charge in which case the L/P switch is doing its job.

Try turning power off to the system for a few minutes and re-starting, that may reset the switch. If it does and the line starts to get cold then locks out agian more then likely a refrigerant problem.

 

you said the fan started. did the compressor also run? you didn't mention it.

 

How can I determine if the compressor is running?

 

You will be able to hear it, if you know what to listen for. The larger of the two refrigerant lines will become cold, provided there is refrigerant in the system.

Or you can simply take an amp reading at the compressor leads

 

Since it appeared that both the CLO and the LP switch were working and that it was likely the compressor was also running I figured that the system needed a recharge and maybe a leak needed to be fixed. Since that was probably beyond me, and with employees melting in the high humidity, I called in a local service guy. After I brought him up to speed, he immediately looked at a cylindrical component inline with the smaller refrigerant line that he called a drier. It was very corroded and clearly leaking. He replaced it and was able to recharge the system. It's up and running again.

While he was there he hosed down the condensers and discovered that the evaporator was plugged up. Either he can come back and clean it or he said I can clean it with an air compressor.

Thanks again for your help. It is much appreciated. Beer 4U2

 

You're welcome.


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