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My heatpump is set to cool but it blows hot air

Customer Question
My heatpump is set to cool but it blows hot air
Submitted: 3 years ago.Category: HVAC
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Answered in 1 hour by:
5/24/2015
HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6,938
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified
Welcome! We keep going until you have all of the information you need.[b/]. Extensive training & coaching also available.
Either the reversing valve is stuck in the heat position, or the electric coil that operates the valve is burned out or not getting 24v power, or the thermostat is defective.
If you have a multi meter and some skill with it I can coach you to a diagnosis, if not tell me which direction you are from the center of the nearest city and I will attempt to locate a well rated service company for you.
.
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Customer reply replied 3 years ago
It has happened two days n a row. Both days I have ten the heat pump to cool and it would run fine all day untill about 8pm, where it would start to blow hot air. I changed the filter and all my registers are open. After some research, I came across a valve problem, but it did work the next day untill nighttime. Would refrigerant levels be low also?
Customer reply replied 3 years ago
I meant I have set the heat pump to cool, not 'ten' - sorry for the typo.
Customer reply replied 3 years ago
I do have a multimeter - a bit of a novice but can follow direction.
HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
Hello again,
If you run the system when it is below 70F outside and it is cool inside. it will cause the cooling coil to develop a huge block of ice around it and stop cooling... that is noticeable by very much restricted air flow, not warm air flow, but no air flow.
We need to look for that specifically.
If the heat pump is going into heat mode, the fattest copper tube connected to the unit that sits outside will get hot... locate that tube and tell me if it gets hot or not and for how long it stays hot.
I need to know all 3 things, where you have the system set and how cool it gets by 8pm outside.
The temperature of the fattest copper tube when it starts to blow hot air and for how long.
And if the fattest tube mentioned gets real cold or frosty about an hour before it starts blowing hot air.
I am going to a dental appointment now, and will be back in 2 hours.
.
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Customer reply replied 3 years ago
As I try to run the system on the third day today, after the initial wait period, The system still seems to be blowing warm air.
The outside temperature right now is about 72° the inside temperature is at 73° and I set the thermostat to cool at 68° to see if it would push cool air. The outside temperature right now is about 72° the inside temperature is at 73° and I set the thermostat to cool at 68° to see if it would use cool air.
Customer reply replied 3 years ago
The large copper tube feels to be cool but not cold. The outside heat pump unit's fan is on and the air coming from the top of that seems cool also.
Customer reply replied 3 years ago
Okay, the system has been on for about an hour or so, warm air is still being pushed out the registers. Outside temperature is 75, indoor temp is 73 and the thermostat is set to 68. The bigger copper tube is neither hot or cold, just cool to the touch (probably normal temp)
Customer reply replied 3 years ago
So now the system has been on for about two hours now and the same scenario: blowing hot air, indoor temp is 72, set for 68, outdoor temp is 74. The larger copper tube is neither hot or cold and the outdoor unit continues to run. I opened the filter door to and the metal fins look normal (a bit dusty but not bad). I am going to turn off the system at the thermostat now.
HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
Hello again, thanks for the information.
If the larger copper tube is not hot, the unit is not actually blowing *hot air, just room air temperature.
Please verify that. If that is actually the case, then the compressor in the unit outside is going off on one of its protective devices.
You typed earlier
"Okay, the system has been on for about an hour or so, warm air is still being pushed out the registers. Outside temperature is 75, indoor temp is 73 and the thermostat is set to 68. The bigger copper tube is neither hot or cold, just cool to the touch (probably normal temp)"
Was the fan on the outside unit running at that time? we need to be very clear on that, either way.
If the fan on the outside unit was running, the compressor is going off on its internal heat sensitive over load.
----------------
To verify that, turn the power off to the outside unit, at that time, not later but right away, make a diagram of the 3 wires that attach directly onto the compressor... then set your multi meter to ohms, and tell me what reads you get between the terminal marked C and the terminals marked R and S.
We can go from there.
.
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Customer reply replied 3 years ago
I am not home at the time. But at the time that I wrote the above quote, the fan on the unit was running.The unit has been off for about an hour. Can I check resistance on the wires when I get back home? About an hour...
HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
There is a ***heat sensitive*** over load built into the compressor, it only trips if the compressor over heats, If the the compressor cools off and the over load closes your test will not prove that the overload is tripping.
The ideal time to check for a tripped compressor internal over load is within 15 minutes of the time it stops cooling, with the outside fan still running.
.
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Customer reply replied 3 years ago
Okay, thanks. So what should I do when I get back to my house? Should I start it back up again and then test what you said above?Like I said before, I ran it today for the third time but this time there is no cool air coming from the registers. The two days before it ran well all day but started pushing hot air in the evening.
Customer reply replied 3 years ago
Question about this service- did my credit card already charged and how many questions (problem solving) do I get? My card will not be charged any extra fees, right?
HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
I am a customer of the web site just as you are, except I answer questions instead of ask them.
With me I work on a no time limit basis for the deposit amount you offered. for any other questions click the 'report question' or 'contact us' button and ask.
.
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Customer reply replied 3 years ago
Okay, thanks for the information.So what is the next step? Do I need to turn the system on again to run any diagnostic tests?
Customer reply replied 3 years ago
So I am home now and the system says it is off at the thermostat. I turned it off 1.5 hours ago. It is blowing hot air. I measured it at the register and it is136 degrees coming out. I am turning off all power at the breakers.
HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
If the large copper pipe on the outside unit is not hot, then it is getting heat from the back up electric heaters if its an electric furnace not a gas furnace.
In that case it is a defective thermostat causing the problem.. 98% chance of that.
If you can take photo's of thermostat terminal strip where the wires attach and a photo of where those same wires attach inside the furnace I can coach you on how to test that.
You can use the 'attach files' link at the bottom left of your reply box to attach those pictures.
.
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HVAC Technician: Phil, Mechanical Engineer replied 3 years ago
Thanks, ***** ***** a proprietary to Trane 3 wire communicating thermostat, the problem is in the thermostat or the control board, but diagnosis without Trane specialized test equipment is not possible.
You can however start by replacing the thermostat, if that solves the problem you are done... If not you will need a new printed circuit board.
Or... you can do this heat stress test on the printed circuit board.
Use a hair drier to slowly and gently warm the card to 120F (warm to the touch but not hot and not over 140F)... if you get any change in behavior that means the card is bad...
A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it.
Constant expansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out.
It is also a good idea to replug all of the connections in the unit, that burnishes any oxidized terminal connections and will sometimes solve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course.
These cards are also damaged by Electrical Spikes caused by power failures and lightning. These high voltage spikes can literally explode the fine 'wire' connections inside the chip. There is also a shunt type device, often printed on to the card that allows a high voltage spike to arc across to ground harmlessly, some of these can wear out after a few times and allow the high voltage spike into the rest of the card and the CPU micro-circuits. The high end printed circuit cards use a large capacitor like device, or several in parallel, to capture and release such surges, these do not wear out.
Let me know how all that goes.
.
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