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Inspecting HVAC Systems Topics include heating, venting, and air conditioning inspections.

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  #1  
Old 8/11/17, 8:20 PM
David OKeefe's Avatar
David OKeefe David OKeefe is offline
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Default Thermostat for heat pump

Today I had to set the thermostat at the EM mode to get the furnace to kick on. It would not work with the heat setting. House had a heat pump/AC unit with a standard/natural draft furnace. Both units were old (20-25 years) I have not run into this before. Thermostats are set to cool or heat, never had to use EM. Do not see many, if at all heat pumps here. Is this normal? Is there something wrong with the way this thermostat is wired or do I need to learn more about heat pumps and how they operate?
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  #2  
Old 8/12/17, 1:48 AM
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Chuck Evans, TREC 7657 Chuck Evans, TREC 7657 is online now
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Default Re: Thermostat for heat pump

With a heat pump system

Heat = Heat pump
EM-Heat = Furnace, electric heat strips, whatever the non-heat pump source of heat is.

So, if you had to turn the thermostat to Em-Heat to make the furnace start, that is normal behavior. Don't forget to test both Heat and Em-Heat modes.



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  #3  
Old 8/12/17, 5:12 AM
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Wayne B. Wilson, TN 439 Wayne B. Wilson, TN 439 is online now
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Default Re: Thermostat for heat pump

It should be a 2 stage , first stage would run the heat pump then the 2 stage the furnace , in the event the heat pump could not keep up .



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  #4  
Old 8/12/17, 8:46 AM
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David OKeefe David OKeefe is offline
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Default Re: Thermostat for heat pump

Quote:
Originally Posted by cevans View Post
With a heat pump system

Heat = Heat pump
EM-Heat = Furnace, electric heat strips, whatever the non-heat pump source of heat is.

So, if you had to turn the thermostat to Em-Heat to make the furnace start, that is normal behavior. Don't forget to test both Heat and Em-Heat modes.
Thank you. Again, not familiar with heat pumps but I always thought they had electric heat strips and not gas hot air. Also I could not read the label on the exterior unit. How would one know that it is a heat pump and not just AC unit without the label?



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  #5  
Old 8/12/17, 9:24 AM
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Charley L. Bottger Charley L. Bottger is offline
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Default Re: Thermostat for heat pump

Quote:
Originally Posted by dokeefe View Post
Today I had to set the thermostat at the EM mode to get the furnace to kick on. It would not work with the heat setting. House had a heat pump/AC unit with a standard/natural draft furnace. Both units were old (20-25 years) I have not run into this before. Thermostats are set to cool or heat, never had to use EM. Do not see many, if at all heat pumps here. Is this normal? Is there something wrong with the way this thermostat is wired or do I need to learn more about heat pumps and how they operate?
Yes ya need to understand how a HP operates if you are going to operate them. Let me explain how I operate a HP and what I check for proper operation.

In this time of the year the unit should already be set in the cooling mode or you should set it to cool if the home is vacant and let the unit run and cool the house down. Once I establish that the cooling mode is performing as intended I switch the stat to normal heat and I only increase the temp about 2 degrees above the temp within the home. This will activate the reversing valve in the exterior condensing unit and the indoor fan in the AHU and or the furnace. The large copper line should be hot to the touch if not the unit is not operating as intended. If you turn the stat up to high in the normal heat mode it will activate the reversing valve and also activate the electrical heat strips.

I then turn the stat to off and observe that the outside condensing unit did indeed turn off. I then set the stat to emergency mode which only activates the indoor blower motor and the Aux heat source which can be a gas furnace or most commonly a set of electrical heat strips. There will usually be two or more strips installed. To ensure that all strips are operating I boost the stat 5 or more degrees above set point I then remove the indoor unit cover and expose the electrical elements. All of the elements are not activated at the same time I then give it a couple of minutes and I check the amp draw on each element. If you don't own a amp meter, go buy one!!!!!! I am posting a PIC of 3 strip elements each element has a black wire connected to one side of the element and yellow wire on the opposite side which also has a round thermal sensor inserted. I check amp draw on each element and I regularly find elements that are not operating. Do not tell me that what I do is above SOP I don't care about that. I care that a HP is operating as the MFG intended in all 3 modes of operation and my clients pay me well for that type of information
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  #6  
Old 8/12/17, 9:33 AM
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Charley L. Bottger Charley L. Bottger is offline
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Default Re: Thermostat for heat pump

Quote:
Originally Posted by dokeefe View Post
Thank you. Again, not familiar with heat pumps but I always thought they had electric heat strips and not gas hot air. Also I could not read the label on the exterior unit. How would one know that it is a heat pump and not just AC unit without the label?
Look down inside the unit most have a reversing valve visible some have the reversing valve hidden. What does a reversing valve look like use google and MR Google will show U a pic of one



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Master HVAC Mechanic Retired
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CMI Certified Master Inspector
Residential/Commercial Inspections
Moisture Intrusion Expert Witness
Okla State License # 130
580-268-3340
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