Heat Pump Inspection

How does everyone inspect heat pumps? I know this has been asked before, but I can’t seem to find the thread I viewed last month. Thanks

Without writing an essay…
Just make sure you understand when and how the electric strips come on and how they can mislead you into thinking the heat pump is working properly when it may not be. There are also new features in units that may change when the strips operate.

Here’s some great HP info from ITA…

David I do not agree with one of the statements that ITA placed on their school info about heat pumps. They stated that if the unit worked in one mode that there was no reason to check the other mode that it would also work. (mode being heating and cooling.) The reversing valve is simply an open or closed valve activated by a 24 volt coil. The coil is normally activated in the heat mode and not activated in the cooling mode and if you do not operate both modes you have not a clue if the coil is working or not.

You gotta point…

Much more involved with modern units than just the coil…

Heat mode uses a lot of circuitry on the defrost board that cooling does not use.

This is true but just checking one mode tells you nothing about the other mode. The valve has to open in the heat cycle no matter what the control device is???


So in the Winter time, I do you inspect Heat Pump in both Modes? Just Defer Cooloing Mode right?

Chuck; you are asking me to stir up a mess right here in front of God and everyone else with that question.

So here is my answer; just depends on the outside ambient. I always start the unit in the winter time in the heat mode this ensures that there is no liquid lying in the crank case of the compressor as heat pumps also have crank case heaters. Compressors are designed to pump vapor not liquid.

I do not run in the cooling mode if the outside ambient is down in the twenty’s or below just a personal choice. Could I; probally so with the unit first being operated in the heat mode. Would you get good readings in the cooling mode; no they would be squirrelly. About the only thing you can accomplish operating in the cooling mode is the fact that you can say yes it does switch from heat to cool. Are you going to blow the valves in the compressor switching to cool my HVAC answer is no.

Sorry I left off an item of concern relating to switching from the heat mode on a heat pump in the winter months to the cooling mode. The unit its self reverses automattically to the cooling mode when ever it goes into defrost cycle with the exception it drops the condenser fan out of the curcuit to bring the head pressure up to help defrost the ice on the condenser

To add…

If you are going to switch a reversing valve in the off season, it should be done at the condensing to you can evaluate it in a very short time. You can’t switch it and walk out doors, or wait for the suction line to get warm way up in the attic.

If you don’t know how to switch the reversing valve from outdoors (way outside the scope of HI Standards) I would not recommend it be done.

So Should we just test it in Heat mode? I didn’t realize you could test heat pumps below in Cooling mode below 60 degrees.

Yes you can check heat pumps in the cooling mode when the outside ambient is below 60 degrees because they have crank case heater and suction line accumulators for protection against liquid migration.

The heat pump changes automattically to the cooling mode when the unit detects a need for defrost it just reverses the flow again and places heat back on the condenser again as it is in the cooling cycle but it drops the condenser fan out of the circuit or simply reduces the RPM depending on the MFG.

David I think was referring to operating a heat pump in the heat mode during the summer months.

Thanks for the response. Charley, what steps do you take when inspecting heat pumps?

Thanks Charlie.
I had to run. Thanks for the good reply.
Yes, I was discussing a “quick test” in the heat mode during summer conditions. We don’t want high head pressures, so it must done quickly.
Winter time testing is no problem (as posted). The heat pump runs in the a/c mode about every 45 min anyway and will not be damaged.


I am lucky if I see a dozen air to air heat pumps in a year here and probally no more than 2 ground source in a year.

I do nothing spectacular over a regular A/C unit. But I do want to see the reversing valve change positions as I don’t want to buy one they can be expensive to change out.

There is nothing an HI can determine about the defrost cycle unless you just happen to be lucky and catch the unit in defrost or unless the unit has a large amount of ice build up on the condenser fins indicating the defrost is not performing as intended. Defrost cycles are generated by an embedded temp sensor within the condenser coil and when the factory non-adjustable temp is obtained it goes into defrost or I suppose this cycle could be generated on these newer units according to run time and a solid state board. In any event the HI should just disclaim the defrost cycle unless you can see excessive ice.

I operate the heat pump generally speaking in both modes heat and cool. Normal on the thermostat. I also check the emergency heat mode and I use my amp meter if the unit has electric heat strips. When I switch to the emergency mode I walk back out to the outside unit to ensure that it is not operating. The two most important items that I am concerned with is the reversing valve and are the heat strips being activated when the unit is in the normal heat mode as I have found this to be the way the installing contrator left the unit wired on numerous units. I use my amp meter again to determine if these strips are activated or not.

For your personal reference only, diagnosis of the defrost system can be performed several ways depending on how intensive you want to get.

  1. You can accelerate the time clock on the defrost board by jumping the two “test” pins.
    You must be ready to yank off your jumper wire as soon as the defrost cycle begins or the accelerated time will kick it right out of defrost again (within a second).
    In order to fake out the defrost board into thinking that the coil is frozen, you must jumper the two leads to the outdoor coil sensor(defrost termination thermostat) before you begin the test cycle, otherwise nothing will happen.

  2. To test the defrost termination thermostat/sensor you should remove it from the circuit board, install your meter to the leads to test for impedance, remove the fan wire from the defrost board so that the outdoor fan does not run. You can just run the unit in air-conditioning or you can accelerate the defrost board into the defrost mode. Once in the defrost mode/AC mode, without running the outdoor fan will cause the oil to Frost up and freeze rather quickly. Your multimeter will indicate the circuit closing as the coil freezes. This will verify the operation of the defrost sensor. You can determine the on/off setpoints of the sensor by converting refrigeration pressures to temperature. Or, use a thermistor on the coil if it’s that critical.

I have never done this procedure during a home inspection, and I see no reason to ever do it. However, I thought you might like the information if you are not aware of it.

If you don’t have gas service to your house in the Tennessee, you have a heat pump around here. Multilevel homes with gas service often have a heat pump for the second-floor in the gas furnaces on the first floor. This saves money and effort to penetrate the roof to vent the furnace from the attic etc.

Also, if you would be interested in a device that easily attaches to the air-conditioning condenser to temporarily modify the air-conditioner so they can be run in the wintertime by cycling the outdoor fan, drop me a private message with your e-mail and I’ll jot down a schematic for you, or take a picture of mine.

David; Yes I knew there was a way to lie to the defrost board but not practical for the HI I just try to keep it simple with most terms that can be comprehended by the average HI.

I will have been retired 5 years this next April from the HVAC business and like every thing else if you don’t use it you loose it.

I know where you’re coming from! :slight_smile:
I’ve been out of it twice as long as that and I scratch my head so much these days I’m starting to go bald!

Oh bald is bad IM’ just gray don’t care what color it turns just as long as it does not turn LOOSE