[axual]

We have a Trane system, a bit over 10 years old. Bought home last year. Has older thermostat.

Running heat now as it's winter here, but noticed that sometimes, the system begins to start, then immediately stops. After checking things, it appears this happens even when the thermostat is off. Sounds like a relay clicking on, then off.

I am not used to heat pump systems and how they operate, and it seems the system never shuts down when it should either, whether emergency heat switch is on or off. When it's on, the Aux heat is used, notably when the temp outside is very cold.

Any suggestions on what may be causing this? Is there relay which would trip on or off, even without the thermostat on?

[hvac1000]

Running heat now as it's winter here, but noticed that sometimes, the system begins to start, then immediately stops

Is the inside starting and stoping or is it the outside or both?

[axual]

With the thermostat set for Emerg. Heat, only the inside unit starts/stops. Seems only the outside unit will come on if Emerg. Heat is set to off (which I'm told is normal). At present, it's about 8 degrees, so I was told that this is too cold for the outside unit to be used to pull heat out.

[hvac1000]

At present, it's about 8 degrees, so I was told that this is too cold for the outside unit to be used to pull heat out.

Yes at that temperature most heat pumps will not work economically.

[axual]

Yes, I understood this to be the case. But this doesn't explain why the inside unit starts for a second, and then immediately shuts down (multiple times over several minutes)... or may start for 10 seconds and then shuts down, even with the thermostats turned completely off.

[hvac1000]

Unless there is a short circuit in the thermostat wiring that would allow a signal to be sent to the unit without the thermostat being turned on I have no idea. It is definitely not standard operation but I know of no specific part in that unit that would cause this to happen unless the circuit board if equipped with one is bringing on the unit with no signal and I would find that hard to believe.

In older non digital thermostats a close set heat anticipator can cause symptoms like this to happen. See below.


Inside the thermostat just behind the outer cover of these types of thermostats you will see a heat anticipator. It looks something similar to one of these two:




These adjustments are the heat anticipator. They are for the length of the cycle of the heating, but sometimes there is one for the cooling. But almost always, the cooling anticipator is a fixed resistor on the subbase. It's a very critical measurement with special instruments for the professional. Don't worry, you can set a replacement thermostat heat anticipator just like the old one or you can make adjustments in very small increments as instructed here.

1. HEAT CYCLE TOO LONG--Set adjustable heater to a slightly lower dial setting. (1/2 division)
2. HEAT CYCLE TOO SHORT--Set adjustable heater to a slightly higher dial setting (1/2) division)
3. YOUR thermostat should look like the picture on the left inside. Use the directions in number 2 since your heat cycle is to short causing a problem with your system. Move the lever just a little bit at a time to the longer side on the little dial till the unit works correctly. It may take a few furnace cycles to balance so do not rush the job by moving the lever to fast. Move the lever and wait 15-30 minutes for the results.

There is a professional way to do this adjustment but involves a meter which you do not have.

NOTE: On digital type thermostats many have a setting program for adjustment.

See this doc.

[axual]

Thanks for the info. I do have a non-digital thermostat (not round, but rectangle) and thought replacing that would be best in the long run anyway, but was not sure. I may start there and then see what the result is. Thanks very much for your information.

[Allen4Val]

Old post