Lennox Compressor wont stay on (help!)

Hello - I was wondering if you could give me some advice. I have a 7 year old Lennox compressor (HP-24 18 or something similar) hooked up to our Lennox heat pump. When I turned on the AC this summer, I noticed that after a day or two, the compressor would shut off, but the blower/fan would keep going, and the compressor would not come back on. Since the temperature starts going up when this happens, the blower never shuts off. If I turn the system off at the thermostat and let it sit for a few hours, it will come on and run fine for a a day or so, but it eventually falls back into this same pattern. It seems like the time it takes to fail is getting shorter and shorter. We have a thermostat provided by our utility company that is all digital, and allows the electric company to cycle our system off during peak demand periods. Would you recommend that I start with the thermostat, or just call an HVAC guy to check it out? Anything I can do on my own to test or fix? I read that sometimes when the unit is low on freon this can happen.

Thanks for any help you can provide.

Kevin Bridges

Hi Kevin, hopefuly, I can sort this out for you.
I'm not familiar with the type of thermostat you have and therefore are not sure how the utility company is accomplishing the prevention of your A/C during peak usage periods. Assuming that this is happening during non-peak usage periods, I would have to say that the problem is with your system.
I would start by using a volt/ohm meter to check a few components of the system.
Check for 24VAC at the coil on the contactor of the compressor. If you don't have voltage there and the thermostat has not reached it's setpoint, then you either have a defective thermostat or a low freon charge. A sure sign that the system is low on freon would a build up of ice on the evaporator coils but, in a forced air system, this is hard to verify because it's hard to get the evap coils. Some systems have a low pressure switch to keep the system from harming itself in the event of a low freon situation. Likewise with a high pressure switch. Make sure your air filter is clean and the blower motor is working as this will also cause an icing condition. Lastly, perform a visual inspection on the compressor contactor. If it appears to be burnt or pitted, it may not be transferring power through the contacts and will shut down the compressor.

Thanks! I'll give it a try tonight.