I just get installed a digital thermostat for my heatpump system. I have an impression that it not control correctly my heatpump. A scenario is my room temperature is 80 deg, I set the desired temperature to 78, and switch my thermostat to Cool. After few delay, the Air handler turn ON but the heatpump fan is not ON and it like that for hours. I ask the tech who installed my thermostat, he told my that I need to set my desired temperature to 77 deg (at least 3 deg difference of my room temperature). I did and its worked, the heatpump kick in and provide cool air. He told me also that in the Heat mode also, I need to set the desired temperature 3 deg above the room temperature to allow the heatpump to kick in.

The question is WHY 3 degrees? My DESIRED temperature is 78 deg, NOT 77 deg. Some experts out there, please help. I wish some explainations.

Thanks

Depending on the make and model of the thermostat, some have programmable adjustable differential settings. Some also have adjustable anticipators settings that you can change. Your service technician should have checked the anticipator set points.

In the cooling mode or heat mode if the temp on a digital thermostat changes one degree the system should come on. It sounds like its wired or set up wrong. The heat anticipator should not need to be set for a digital t-stat. I have a heat pump the temp is set on 73 the temp reading may move one degree before the system comes on.

Most digital thermostats don't need the anticipator reset but not all installations are the same and that's why many of them have that option available. The length and size of the thermostat wire, reversing valve coil and transformer voltage all effect the anticipator. If you set the stat to a lower temperature and it works fine, then its most likely wired correctly.

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Originally Posted by hq62063

I just get installed a digital thermostat for my heatpump system. I have an impression that it not control correctly my heatpump. A scenario is my room temperature is 80 deg, I set the desired temperature to 78, and switch my thermostat to Cool. After few delay, the Air handler turn ON but the heatpump fan is not ON and it like that for hours. I ask the tech who installed my thermostat, he told my that I need to set my desired temperature to 77 deg (at least 3 deg difference of my room temperature). I did and its worked, the heatpump kick in and provide cool air. He told me also that in the Heat mode also, I need to set the desired temperature 3 deg above the room temperature to allow the heatpump to kick in.

The question is WHY 3 degrees? my DESIRED temperature is 78 deg, NOT 77 deg. Some experts out there, please help. I wish some explainations.

Thanks

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If the blower runs at a 1 to 2 degree difference the heat pump should too. Blower running and not the heat pump I would say stages wired wrong on t-stat. second stage kicks in on the 2 to 3 diff. If you change the heat anticipator it will only give you a longer or shorter run time per cycle of your system.

Check your thermostat manual or find one online and look for something called a swing mode. This will tell the thermostat how many degrees above the set point it will turn on and off.

What kind of new thermostat do you have? (make & model) Fan delay is usually because of the blower time delay sequencer in the air handler and nothing to do with the thermostat.

A heat pump is a kind of refrigeration unit. As such, the compressor cannot be coming on within 5 or 10 minutes of going off. This causes a vapor lock in the system. If the controls allowed the pump to operate the pump would maintain the vapor lock condition forever. This would mean that the pump would stay on and you would not get heating or cooling. You would, however, be paying for the power 24/7 to do nothing. The air throughout your home is probably 3 degrees or more from place to place in the same room. So the slightest air movement would be causing the pump to try to cycle more often than the pump can handle. That is why the controls are as they are.

If you set it for 78 degrees, it will come on at about 80 in the cooling cycle and go off at about 76. If you could have a system that kept it exactly 78 degrees it would be cycling every 5 minutes or so. The way electric motors work they draw the most current at start up. That would mean very high electrical usage. That is why even electrical resistance heaters have about 3 degrees in difference between starting and stopping. Ceramic heaters are the only ones that do not as they vary the resistance in the heating element. But they do not cool.

A heat pump is a refrigeration unit. ( compressor, evaporator, condenser, metering device ) Most systems have built in time delay for several reasons. When a compressor shuts off, the system needs time for the refrigerant to balance out equally between the High side and low side. If you attempt to restart the compressor with high head pressure it will probably go off on internal overload. Short cycling also is bad for the contactor causing unnecessary arching. Most thermostats have a build in time delay to stop the this from happening as well as the condensing unit circuit boards on heat pumps. This complaint states it was hours before the cooling came on which would indicate the fan switch was in the "on" position and the room temperature was still under the thermostat set point or the thermostat is out of calibration. When he lowered the set point everything worked fine.

Thank you all. I spoke with the tech and he show me a quote in the thermostat user manual "How to test the thermostat"

1- Put the mode switch to cool position.
2- set the target temperature to at leat 3 degrees below the room temperature. The air conditioning system and the fan should turn on within few seconds.

For the heat mode, essentially, the manual said the same thing except set the target temperature at least 3 degrees above the room temp.

If I do the above, everything worked fine. If the target is set only 1 or 2 degrees below/above the room temperature, then ONLY the air handler worked, the compressor (out side unit won't kick in). So, the tech told he wired everything correctly, and that is the way it worked, I need to set 3 deg above/below.

My thermostat is from ICM Controls, model SC 2200.

Quote:

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Originally Posted by hq62063

Thank you all. I spoke with the tech and he show me a quote in the thermostat user manual "How to test the thermostat"

1- Put the mode switch to cool position.
2- set the target temperature to at leat 3 degrees below the room temperature. The air conditioning system and the fan should turn on within few seconds.

For the heat mode, essentially, the manual said the same thing except set the target temperature at least 3 degrees above the room temp.

If I do the above, everything worked fine. If the target is set only 1 or 2 degrees below/above the room temperature, then ONLY the air handler worked, the compressor (out side unit won't kick in). So, the tech told he wired everything correctly, and that is the way it worked, I need to set 3 deg above/below.

My thermostat is from ICM Controls, model SC 2200.

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Sounds to me your getting the run around. If the blower is on at 1 to 2 degree diff . The heat pump should to. Tell them your unhappy with the T-stat and that its not working right and to send a different service tech to check it out. If not try a new company have them write down what was wrong and show it to the firsts company. It only takes one bad apple to spoil the bunch. Good luck.