unit cycles on and off multiple times in heat mode

by Jim Mundy
(Ruckersville, VA)

I have a Rheem model RHLL-HM3617JA that when in heat mode will cycle on when the thermostat calls for heat. Then the outside unit kicks on, but then turns right off or after a several seconds. This happens sometimes three times before the unit stays on and delivers heat. This condition seems to happen more often when the outside temperature is below 35-36 degrees.

I have had the company who installed the system back at least 4 times. The first time this happened they replaced a bad valve, (not sure which one). The last time the coil in the air handler was leaking and had to be replaced.

The above condition still persisted after the coil replacement. The owner of the company came and tried to troubleshoot the problem and adjusted the position of the defrost unit. This changed the duration the unit ran before cycling off, but didn't correct the same basic problem. Before this adjustment the unit would run maybe 20-30 seconds before cycling off and then back on. After the defrost adjustment it now is only a few seconds or it doesn't fully turn on before it shuts off. The sound it makes some times is best described and being similar to air brakes on a truck releasing.

This has been very frustrating for me and I'm sure my heating and air contractor. Any help you can give will be greatly appreciated.

As a side note, the contractor that installed the system comes highly recommended and seems to be knowledgeable about his business, so I don't think it is a problem with him not knowing what he's doing. After the initial installation a couple of years ago I have been dealing with the owner and not his technicians.

Thanks again,

Jim Mundy

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Dec 09, 2013
by: Anonymous

Based on your assessment, it seems that your problem is tied common problems faced in cold weather. You said that the owner "moved the defrost unit". It would be interesting to know what you mean by this. I would be surprised if something associated with defrost was causing the problem, since it shuts off so fast (too fast for defrost to resolve the issue)

A few possibilities.... (simplest solution first)

- dirty air filter or coils
- unit is low on refrigerant charge
- there could be a bad sensor that is incorrectly faulting out the unit
- faulty reversing valve or hot gas bypass valve
- faulty control relay that is not switching upon start up of the unit

There is a nice troubleshooter available at the following url: http://www.heat-pump-pro.com/heatpumpproblem.html.

This might help you. But more details regarding the movement of the defrost unit would help, as this seemed to make the problem worse.

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