Heat Pump Short Cycling to Hold Temp.

Hi all, I have a roof mounted heat pump that when in the heat mode it appears to cycle normally until it reaches the set temp on the t-stat, then it really short cycles to hold the temp.

Once it reached the set temp it will cycle on for about 6 minutes and then off for only 3-4 minutes before cycling on again. If i increase the t-stat a couple degrees warmer it appears to cycle as it should until it reaches the new desired temp. I suspect it's t-stat related but plan to call my AC guy out to take a look. Just curious if there is anything obvious that would be causing this ? It does not let it drop a single degree before cycling on... shouldn't there be a degree or 2 fluctuation?

T-stat is a Honeywell IV.

One other item, it appears to defrost more than it should - 2-3 times during the morning after I turn it on to warm the house up.


Any insight? This is my first winter in this house.

SOme thermostats have the ability to program them for the type of heat you are using...ensure if yours does that it is set to indicate it is controlling a heatpump. Some can also enable you to set the hysterisis of the heat control (i.e., to let it swing more). If the house is cooling off enough in 3-5 minutes to trigger the thermostat, you need to find the air leaks and maybe beef up the insulation, though, unless it is sitting in a drafty area. Placement of the thermostat can sometimes be critical.

It does not cool off in the 3-5 minutes between cycles.. I can decrease the temp setting a couple degrees and it takes a long time ( almost a couple hours ) to drop enough for the unit to cycle on again. The house is older but has great insulation, teh temp does not even need to drop (according to the t-stat reading ) for the unit to cycle back on.

I find myself having to manage the t-stat.. turn it up to 2* higher than I want and when it passes the desired temp, set it for 1* below what I want... otherwise it short cycles and does not increase the temp of the house at all.

It almost has to be the hysteresis adjustment.

The electronics can detect much smaller temperature differences than a whole degree, so depending on how it is set, it is trying to maintain as close to the set point as possible. If you tell it it is a heat pump (and not say the strip heaters), it should be less aggressive in trying to maintain exactly the setpoint.

jadnashua said:

If you tell it it is a heat pump (and not say the strip heaters), it should be less aggressive in trying to maintain exactly the setpoint.

Click to expand...

OK. I walked up to it and said " you are a heat pump" and it ignored me


How do i set it to "heat pump" ? Do I need to take the face off like I was changing the batteries?

Phillbo said:

OK. I walked up to it and said " you are a heat pump" and it ignored me


How do i set it to "heat pump" ? Do I need to take the face off like I was changing the batteries?

Click to expand...

Which EXACT model is the thermostat? Is it from the Honeywell Chronotherm- IV series? If yes, it already knows it's a heat pump, and has a programmable hysteresis. Some variants had a "learning" function to limit overshoots & short cycling as well. Dig up the manual (it might be online, might not.)