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Problem with Auxilary Heat turning ON.

HowardZ Member Posts: 15
edited February 2021 in Thermostats and Controls
I hope I am not too wordy, but I will give an introduction.
My Heat Pump guy (Harry) installed my HP Around year 2000 to 2005. Outdoor is R22 Trane, furnace is Carrier (He installed both) - single family house (located 20 miles NE of White House, DC). Due to changing refrigerants and possible shortages, I paid him extra to buy a metal bottle of R22 - to put my name on it, and it is only to be used for my system.

He tells me he is dying from COPD, can't do house calls, can't even talk very long on the telephone. He has a strong accent, but I usually can understand him. He says he has referred customers to 10 different local HP service-persons. After the visit, he calls and asks what they did and what they charged. All were over $$$ for a one hour service call. He says it should be $$$ to $$$ per hour plus parts. They are all crooks, and he can not recommend anyone. Also due to COVID-19, and my being an old man (highest risk of dying from COVID is being an old man), I really don't want a service-person coming into my house.

Four years ago I had runaway Auxiliary Heat. Harry talked me through it. First, disconnecting the wires going to the strip heat and putting electrical tape on the tips.
Ordering parts on the internet, and replacing the relay and its little reticifier board that rides on top of it. All is well again.

Two years ago, I had the same problem. Replaced the relay and rectifier board. All is well again.

Now I have a very strange problem.
The auxiliary heat will not come on. I keep the thermostat at 65 F. During cold weather, the thermostat displays Aux heat is on, but it really is not, and sometimes indoor temperature can go below 60 degrees while the HP runs hour after hour without stopping.
I verified that the air coming out of upstairs vent is under 80 degrees using a Fluke Meter with a temperature sensor.
Then I change the thermostat mode to Emergency Heat, the outdoor unit stops. And the aux heat is working - with air coming out of the vent over 90 degrees, sometimes over 100 degrees.
I love my Bryant programmable thermostat with outdoor temperature sensor. I have two of them. It doesn't matter which thermostat I use - same behavior.
I ordered additional relays and additional circuit boards.
The relays came (still waiting for the mini circuit board).

I have a plug in 34 volt A/C power adapter - and used it for bench testing.
The Original Relay and its mini circuit board - Normally open relay - both legs of the relays should have infinite resistance, and when activated have near zero resistance. Without being activated - one leg has some measurable resistance - was high, but should have been infinite - and half of this relay certainly died and caused the runaway heat problem 4 years ago.

The Relay I replaced two years ago - it seems to work fine during my bench testing. But it is possible that when in use - heat might cause electronics to fail. (I know from the infamous Volkswagen Relay 109 problem in my previous car).

So, I took the mini board from the original relay which was pulled out 4 years ago, along with a new relay (new mini boards are stuck at USPS locations understaffed due to covid). I installed it and no change in symptoms. No Aux Heat, unless the Emergency Heat mode is selected which turns off the outdoor unit.

Then I did something potentially dangerous. I raised the thermostat set point temperature, Aux Heat is displayed, I took off the top furnace panel, I put my fluke on the Relay's DC Terminals - and I only got around 21.75 volts DC. This relay needs 22 volts DC to close (and activate the Aux heat). The risk was I could get electrocuted if I touched the wrong connectors while everything is running.

The part number from my old mini-board has been superseded with a newer part number. When a part number is replaced with a newer part number - either they figured out a cheaper way to manufacture it, or they improved the part. The mini-boards I am waiting for are the newer part number - waiting for them to be delivered.

Then today, I got another idea. I again bench tested the relay and mini-board which I had taken out a few days ago (it was in use for the past 2 years). I measured the A/C voltage going into the miniboard (27.4 Volts AC), and the D/C voltage going into the relay (22.9 Volts DC). There is a 4 1/2 volt drop. The only thing this mini-board has is 4 diodes - probably a simple rectifier circuit to convert A/C to D/C. I think the voltage drop should be 1 to 2 volts, not 4 1/2 to 5 volts.


  • HowardZ
    HowardZ Member Posts: 15
    I found the T92S7D22-22 relay specifications:


    It should activate at 16.5 volts DC, and release at 2.2 volts DC.

    So, the voltage drop should be OK.
    JUGHNE Member Posts: 11,056
    How many stages of electric aux heat do you have?
    Possibly there are 2 stages.
    The tstat aux notice shows to turn on the first stage on to assist the HP.
    The second stage may come on only when you go to emg heat.

    Possibly tstat could be re-programed to bring on third stage when it wants aux heat in normal HP mode.
    1st stage is HP, 2nd stage is first stage of electric elements, 3rd stage is second stage of elements.
    Just a wild guess.
    Wear leather gloves, stand on a rubber mat, wear glasses and don't get electrocuted!
    The old idea to keep one hand in your pocket has saved me many times.

    Hope you get your R-22 back someway.
  • HowardZ
    HowardZ Member Posts: 15
    edited January 2021
    thanks for replying.

    I believe the thermostat is wired:
    RED 24 VAC HOT

    There is only one relay for the strip heat.
    Both strip heaters have one wire each which go to the relay.
    However there are several additional wires on the relay - not sure what they are for.
    When I replace the relay I just move the same wires to the same relay connectors.

    The Carrier furnace also has a control board (perhaps 5 in X 5 in) with an automotive fuse. Do you think replacing this board might help?

    BTW, I know nothing about doing any work on the outdoor unit.
    My only fiddling has been replacing the relay and its mini-board.

    I looked and this Bryant TSTAT thermostat has 4 dipswitches - all are OFF.
    The 4th one is for 3 stage heat.
    I opened the thermostat, Put the 4th dip switch ON and then OFF - just to make sure it is OFF.

    From the manual:
    This switch converts a 2-speed heat pump thermostat with 1 stage
    of auxiliary heat into a 1-speed heat pump thermostat with 3 stages
    of auxiliary heat for comfortable leaving air temperature. It
    requires selected heaters with 2:1 ratio element sizes plus FK, FV
    fan coil. Refer to variable-speed fan coil literature for details.
    TO SET:
    OFF—for normal 2-speed operation. This is factory default.
    ON—for intelligent 3-stage heat with FK, FV fan coil.
  • HowardZ
    HowardZ Member Posts: 15
    I think I solved the problem - will take a few days to be sure.
  • HowardZ
    HowardZ Member Posts: 15
    edited February 2021
    Years ago, I added a second thermostat for the finished basement. I find it best to control heat in the basement with the right registers opened/closed - resulting in the entire house staying within 5 degrees. Upstairs is best for controlling AC with almost all the basement duct registers closed. I press the mode button several times to turn OFF one thermostat, while the other is controlling - to avoid any conflicts - because this is not a zoned system - the two thermostats are wired together controlling the furnace. Yes, several years ago Harry winced in disapproval.

    With the current problem, I took one thermostat and kept it swung open, so it is not even powered on. Swung open is where one installs the thermostat with the small wiring block screws exposed.

    Well, when one thermostat has heat turned on (but not Aux heat), I went to the other thermostat to measure AC voltage between the black(ground) wire and the others. Every single wire has power. Not just Heat, Aux Heat, Fan, but even the Orange air conditioning wire. When placed in emergency heat mode, the only wire that is hot is the White Auxiliary Heat wire - as it should be.

    My first thought was the thermostat was broken. So I swung open that thermostat, and put into operation the other thermostat. Exact same behavior is observed with the Fluke meter measuring AC voltage.

    So, I am concluding that whenever the outdoor unit is activated to produce heat,
    the outdoor unit's defroster board is:
    activating the reversing valve (Air conditioning)
    activating indoor auxiliary heat
    NOT turning off the outdoor unit's fan.

    Can you imagine the outdoor unit being in Air Conditioning mode all the time, and the indoor unit using Auxilary heat all the time. No wonder I have high electric bills. This sounds crazy - do you think this is possible?

    There was snow today - high was 31 degrees today - and the defroster cycle apparently did work to eliminate a thin layer of snow around the unit (I didn't observe the defrosting cycle when it happened - just assume it worked).

    I can do additional testing, by opening the furnace during operation to check for voltage at the aux heating relay - to verify that aux heat is on at all times when regular heat is called for by the thermostat. However, doing this is risky, and I think the problem is the outdoor unit.

    Another possibility is a wiring problem - causing shorted wires at the outdoor unit.

    So, I plan to get a professional to check the outdoor unit's defroster system, and replace parts as needed. Hope he will not need to enter the house, but if he must I will give him two new masks to wear (KN95 + surgical masks).
  • HowardZ
    HowardZ Member Posts: 15
    edited February 2021
    This morning I placed aligator clip wires onto the auxiliary heat relay - then to my fluke.
    When thermostat turns heat ON, but not showing auxiliary heat being turned on - the fluke meter showed 21 1/2 volts. This means every time the outdoor unit is on (fan moving) that the auxiliary heat is on.

    After shutting things down, I removed the two wires going from the relay to the heat strips, and covered the connector ends with electrical tape (to make sure they don't touch anything). Now the heat pump is blowing out air from the duct at around 50 degrees F. while the room is at 60 degrees F..

    I waited 10 mintues - and is 62 degrees air coming out of the vent.
    I closed the furnace cover - and now 74 degrees air coming out of the vent.
    So, I think the A/C on and Aux Heat Relay being ON - was a normal defroster cycle.

    Problem is email from my electric company says my electricity usage this winter is 134% higher than similar homes in my neighborhood. My electric bills have been over double what is normal. Latest email from my electric company says - based on my usage the electric bill will be $756 ($471 more than the same time last year).

    So, I am going to watch the air duct temperature.
    I suspect a malfunction where it goes into defrost cycle way too often.
  • WMno57
    WMno57 Member Posts: 1,253
    Do HVAC systems have 24v DC?

    I would have guessed:

    240v AC
    120v AC
    24v AC for the controls and thermostat
    5vDC or 3.3vDC for the computer electronics

    Am I wrong about the low voltage for the electronics? Do HVAC circuit boards run on 24vDC?

    I DIY.
  • HowardZ
    HowardZ Member Posts: 15
    Everything seems to be 24 volts AC.
    But the relay which turns on the aux heat strip heaters - is a 22 volts DC relay - so there is a small rectifier mini-board which converts AC to DC - just for the relay to operate.
  • HowardZ
    HowardZ Member Posts: 15
    I have come to the conclusion that the Defroster control board is turning on auxiliary heat and also air conditioning while leaving the outdoor unit's FAN turning. This goes on for long periods of time. I measured 30 minutes and still going - but then switched to emergency heat mode.

    I am going to try to get a professional to change the Defroster control board, and while he is at it, maybe the two sensors too.
    JUGHNE Member Posts: 11,056
    This is how "old school" heat pump defrost works. Todays units still will follow this procedure with some refinements. But produces the same results.

    When your defrost board initiates a defrost, it does because a sensor in the outside coil has been below a certain temp for a certain amount of time.
    So it switches the reversing valve to the AC cooling mode, (usually with a "whoosh" sound as it reverses).
    The board then shuts off your outside fan so the outside coil (now in AC mode) gets hot quickly and melts any ice that has accumalted. Then when sensor feels warm temp it switches back to heating mode...again with the "Whoosh" sound as the reversing valve switches. And the outdoor fan turn back on.

    But when it goes to defrost mode it will activate your aux heaters. This keeps from blowing cold air in your house as your system is now in the AC mode....taking your heated house air to aid in melting the outside coil.
    This usually happens quickly and then things go back to the heating mode.
    However is the outdoor fan does not shut off then the outside coil will not warm up quickly and may run a long time to defrost. Meanwhile it would seem that the AC is running and the aux heaters are running to counteract the cold air produced.

    Usually inside the cover of the HP/AC unit there are instructions to test the defrost board.
    Also may be methods to increase the times between defrosts.
    FIRST....turn off the outside 240 volt power and also the inside power to the air handler.
    You can short out the 24 vac system and have more problems.
  • PC7060
    PC7060 Member Posts: 1,156
    @JUGHNE You can short out the 24 vac system and have more problems.”

    been there 
    JUGHNE Member Posts: 11,056
    Yes, about 3 weeks ago I was testing a defrost board, shorted out the 24VAC. Of course everything stopped....I know what I did. Changing a fuse is usually not a big deal. But this was an air handler in the attic....50' crawl thru insulation, cut open foil tape sealing the AH, replace fuse, reseal the air handler with foil tape and then the return crawl.
    All the time wondering how in the hell I ever installed two 2 ton air handlers and all duct work up here about 20 years ago. Also thinking how to coax my friendly competion into changing out the R-22 systems when the time comes.

    Very careful after that testing the board.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    @JUGHNE, That sounds like you might have said "The guy who has to work on this is going to hate me" 20 years ago!
    Ask me how I know?
    I'm retired now and in the last 10 years, I have installed less and less of those jobs, moving crawl space systems to garages and attic systems to closets whenever possible.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • HowardZ
    HowardZ Member Posts: 15
    edited February 2021
    Well, I had a professional come today.
    He said the refrigerant was low - he used my R22 bottle.
    He said he couldn't get any refrigerant in, asked me to change the thermostat to A/C.
    He turned the bottle upside down, he shook it.
    He still didn't know how much refrigerant he put into the system.
    Inside the house he measured 55 degree air going into the furnace, and 74 degree air going out and said he must have put enough in.
    He had the side cover off which has written tables - but apparently he could not use the tables?

    I asked him to test the defrost board.
    He shorted the test pins - nothing happens.

    He charged me $$$ to for the service call.
    He said call him back when the weather is warmer (it was around 40 degrees today) better so he can put in the correct amount of refrigerant.

    He called his boss with my model number - BTW it was not a Trane, it is a Payne (my error).
    If I want the defrost board replaced - it will cost $$$ (parts and labor).
    He recommended to wait and see if the unit ices over to know if the defrost board needs replacing, and call if it needs it. He says a defrost cycle can still happen without the fan stopping.

    My sick HP guy, who says he is dying from COPD and can't make service calls, says this repair guy (George) is an idiot. He should have no trouble adding refrigerant. He should have no trouble checking the defrost board. Harry says the FAN must stop during a defrost cycle. Harry says this guy George is an idiot, a beginner. They charged me for an expert, and sent me a beginner. And $$$ is way too much money to replace the defrost board.

    I photographed the defrost board, it is part number HK32EA001. I can buy it for around $100 on the internet.

    If it needs replacing - I will do it myself.

    Harry says I should also change the coil thermostat sensor, but I don't know the part number. Maybe it is this one?

    I will research how to test the defroster board.
    Or wait for the HP to frost over in the near future.

    Outdoor model# PH10JA036-E

    Any advice?
  • Illinoisfarmer
    Illinoisfarmer Member Posts: 52
    First of all, I'm not a pro - so take everything I say as the ramblings of a complete and total novice.

    I don't think we're allowed to discuss pricing on here, which I totally respect and agree with. But based on some personal experience, I would offer the following observation...

    You've got a system that is between 16 and 21 years old, and uses R-22. Since it was low on charge, that refrigerant has gone somewhere, sometime. True, you own a cylinder of R-22, and let's face it, that was an excellent investment - I personally put everything into Blockbuster Video stocks - but if you do indeed have a leak, it would likely require the evacuation of the system to repair, and your valuable R-22 might not be enough to get the job done.

    The outdoor unit that you reference, PH10JA036-E, seems to be a 10 SEER Unit. I'm not in the trades, but it appears to me that you can do MUCH better efficiency wise. Like almost twice as good.

    I have some experience with the auxiliary heat 'running wild', so I know your pain here. Unfortunately, no one noticed that the heat pump wasn't running until the kindly Electric Coop sent me a bill that was, like yours, nearly double. They are dependable that way.

    With all due respect, and I am not casting any aspersions on your problem solving or situation, it looks to me like the system has served you well for its normal, expected life. It appears that you might be able to pencil out a new, more efficient system for about the same cost as your high power bills and the repairs that you may already need - not even considering what you might have headed your way in the future. You also may be able to do a bit of horse trading for that cylinder of R-22. I think there are a lot of people that might work with you on that.

    Finally, and again with respect, I can totally relate to your conversations with Harry. Our Harry was Hubie, and he passed away from COPD and cancer a few years back after working on my familys' HVAC units for a couple generations. Hubie would have used MUCH more colorful language than 'beginner at an expert rate', but I can hear him saying the same thing.

    Have a good evening!
  • HowardZ
    HowardZ Member Posts: 15

    Thank you for your nice comment.
    Very few respond to this thread.
    It is more of a way of documenting my thoughts and experience.

    I found a youtube video on how to test my exact defrost board.

    Maybe I will test it tomorrow.

    Yes, this HP has been in use probably 15 to 18 years old.
    It was manufactured in 2003, but might have been in inventory a few years before being purchased.

    I forgot how much the last HP cost me, but it was many many thousands of dollars, indoor and outdoor units were replaced. If I worked a good job, replacement might be a good choice - throw some money at it and not worry about it for many years to come. But, I have not had a professional IT job in over a decade.

    I did an internet search.
    Difference between SEER 10 and SEER 16 is $591 in yearly electricity savings.
    The website says it is not worth paying extra for SEER greater than 16.

    If I can spend some time and a few hundred dollars keeping it going a few more years, I think it will be worth doing. After COVID is all over with, I might even take a class in HVAC. Then with a few specialty tools I will be able to add refrigerant myself.

    I can only remember Harry adding R22 one time. But, I might not be remembering correctly.

    But, if it needs extensive professional repair (like repairing a leak) - the people here just can't do a job right, and charge 2x or 3x what they should. So, in that case a new HP might be the way to go.

    I have so many unexpected negative things happening at once - I might not get to the defrost board right away.

  • HowardZ
    HowardZ Member Posts: 15
    The ending:
    I got a guy who works for a local county doing AC repair for over 20 years.
    He replaced the Defrost Board, sensor, and capacitor.
    Price was approximately 1/2 the other guy.

    I keep watching for the problem to recur.
    Also watching for a defrost cycle to occur.

    I think all will be well.

    BTW, the capacitors are cheap and easy to replace.
    How often should I replace the capacitor as preventive maintenance?