HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On - HVAC - Contractor Talk

HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On

 
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Old 06-02-2011, 08:14 PM   #1
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HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Arcoaire 3ton HP, sorry model and serial #'s to faded to see.
Been called out twice on this and have yet to narrow down anything as system is normal. Here goes...
When HP is in air conditioning mode, RV energizes on Cooling mode as normal. But sometimes while unit is in air conditioning mode, something causes system to start blowing warm air. (the HP is still running per tenant as I have asked them to check condenser) When I get there, I check pressure, they are in normal range, 72 L / 225h no pressure fluctuation . Condenser and evaporator coils are clean.
I have been looking at other options, as in bad RV coil, board, valve, t-stat thinking 24v is dropping off somewhere or RV is bad. But can't find anything while testing. I have checked wiring and voltages. Just wondering if anyone else out there has experienced this condition. And what I am missing
Thanks
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Old 06-02-2011, 09:17 PM   #2
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


You are listed as an electrician what experience do have on heat pumps? Could be an intermittent RVS solenoid or as you say electrical wiring. Connecting O terminal to R terminal will keep RVS energized without thermostat for troubleshooting. If problem disappears then you need to check thermostat wiring. If the problem continues with O connected to R and heat pump you can then do the same at thermostat. If problem goes away the problem is in the wiring. If it goes away it is in the thermostat. Many times with solid core wire there is always a possibility of a cracked wire that is causing intermittent problems.

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Old 06-03-2011, 07:19 AM   #3
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Thanks Mech, my profile list electrician but also a Mech Cont, been one for over 20 years, Guess I need to change that profile so I don't get the heave- ho -what- for-discussion. I generally work on chillers but occasionally will look at residential air for friends and for my rental properties.
Anyway, I appreciate your response and will energize the valve as a means of troubleshooting.
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Old 06-03-2011, 03:06 PM   #4
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Sometimes when the comp stops running due to overheating (motor quitting, refrigerant low, bad cap) they people will describe it as hot air as if the heater is on where in fact it's just ducts picking up heat from the attic and so on.

I would consider looking for a weak capacitor to the comp, bad start assist, contactor, outdoor motor, refrigerant etc. Anything which would cause the comp to open on IOL or fail to start.

I'd be sure a short isn't bringing on the heat strips.
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Old 06-03-2011, 07:57 PM   #5
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Probably a bad defrost sensor. The defrost board basically doesn't know if its in heating or cooling mode, it only knows to defrost when the defrost sensor.stat says its cold enough and the timer times out.
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Old 06-03-2011, 08:43 PM   #6
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Mech, thanks for the heads up with energizing/ tying together O&R. I hope to remember that one.
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Old 06-03-2011, 08:59 PM   #7
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


B.T., thats a good one to remember as well. I would suspect maybe a short to the elements, but that's just throwing a dart
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Old 06-04-2011, 06:06 AM   #8
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Quote:
Originally Posted by flashheatingand View Post
B.T., thats a good one to remember as well. I would suspect maybe a short to the elements, but that's just throwing a dart
Sometimes throwing a dart works pretty good. And over the internet, we're all throwing darts on limited info questions.
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Old 06-04-2011, 08:08 AM   #9
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Darts would surely short out the wiring.
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Old 06-04-2011, 08:34 AM   #10
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


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Darts would surely short out the wiring.
LOL... My aim with darts isn't always good. I probably would end up hitting the condenser coil.
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Old 06-19-2011, 12:32 PM   #11
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Update...
Thanks for all the info. Being an intermittent problem I took a step back and started diagnosis all over again. It had been 4 days since it happened again so I loaded up the tools and headed over. The weather has been hotter than heck the last few weeks and I knew the system had been running almost constantly during the days, so this added to the question as why it only occurs every once in a blue moon. and as usual, it never happens when I got there.
I ruled out IOL after testing fan, cap and compressor. Next, I am thinking if the system continues to run, as she says, its either low voltage problem, circuit boards, or heat strip relays. I amped, ohmed, probed and tested everything in sight. Good thing the tenant wasn't hanging around otherwise she probably would have been tested to. Nothing.
So back to the air handler in the 120 degree attic. I get out the technical tools..my fingers...start moving wires around to see if everything is tight. CLIck Click click...okay on to something. Click..heat strips on, click they go off. Trace to circuit board. Just for kicks and giggles I jiggle the air handler..click click.
Pulling the CB, I noticed small piece of bare t-stat wire was laying under the board. Also small scorch marks on board where wire had been. Could this be it? Replaced board and so far its been 8 days and no call. I have no hypothesis to share on this..Maybe a fluke?
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Old 06-19-2011, 02:22 PM   #12
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Quote:
Originally Posted by Happer View Post
Replaced board and so far its been 8 days and no call. I have no hypothesis to share on this..Maybe a fluke?
If no failures for 8 days you can be 95% confident that the problem is gone if, before the fix, it failed once every 60 hours or so. If it failed less often then it's less than 95% confidence.
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Old 06-19-2011, 02:49 PM   #13
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


You probably got it.
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Old 06-19-2011, 06:05 PM   #14
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


As B.T. said, you probably got it, but, possibly could have saved a few bucks by just fixing the bare wire...... Who knows, not there, and just throwing a light hearted jab. Thanks for the heads up, as all us us benefit from hearing the outcome.
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Old 06-19-2011, 10:12 PM   #15
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Re: HP Occasionally Kicks Into Heating Mode While Air Conditioner Is On


Good find. Many times on intermittent problems we don't go the extra step to checking each and every connection.

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