Heat pump defrost control board and thermostat reversing valve voltage level

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(Sent here from alt.hvac)
Does a heat pump's defrost control board change the voltage level seen at the thermostat on the reversing valve lead?
When in heat mode but blowing cold air, the reversing valve voltage at the thermostat is 0V as opposed to 26.6V when working properly.
My heat pump puts out very good heat but it also seems to love to periodically blow cold *far* more often and for *far* longer than I'd expect to be due only to the defrost cycle. (The unit does not have resistive heater strips). Sometimes it seems to get "stuck" blowing cold for hours and sometimes it blows cold at least 50% of the time.
I'm trying to determine if the thermostat or the defrost control board has gone insane.
A tech came out recently and could find nothing wrong with the heat pump. The refigerant level was perfect and its diagnostic board reported no problems. It is a trane. It was of course not misbehaving when he was here.
This is Arizona and therefore only about 50F with low humidity.
Also, the heat pump, during summer months, sometimes does the opposite. It will blow hot air when it should be blowing cold.
Thanks in advance for any help.
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Please don't buy into the crap from the psychopath paul and his possee at alt.hvac.
Keep ypur posts into alt.hvac and you'll actually get answers.
Kill file paul and his possee.
--
Jim McLaughlin

Reply address is deliberately munged.
  Click to see the full signature.
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A heat pump blowing cold air 24/7 does not mean it isn't working properly. It has nothing to do with the low voltage circuit.

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Oh shit! Now that's funny, "BoB" Bubba

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wrote:

Boob is more like it.
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are you on crack?
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The supply temperature of an air to air heat pump will feel cold because it's lower than your body temperature. He has no back up heat, so the air never feels warm. In a typical tract home where the builder hired the low bid HVAC contractor, the duct work may be too small, so the velocity of air coming out feels even colder because of a wind chill effect on the body.

it
pump.
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OP here.
Thanks.
However, in this case, it will blow as cold as when in AC mode for very extended periods ( much longer than defrost cycles ).
So cold for so long that the whole house gets gradually colder instead of gradually warmer.
I'm really curious if the defrost circuit is bad or if the thermostat is insane.
When the heat pump desides to start blowing cold, the voltage at the reversing valve lead at the thermostat goes from 26.6V to 0.0V.
Is this voltage change due to a "command" from the defrost control circuit?
Can the defrost control circuit even drive that voltage level?
If not, It would seem that the cold is due to the thermostat loosing its mind.
Again, thanks for any help.
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Two words: reversing + valve.
Bob wrote:

air
low
air
circuit?
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Most units (not all) have a board that will only allow so long of a defrost whether it's done or not. Not saying that it ISN'T getting stuck in defrost, but not likely. Could be the reversing valve not "opening back up" all the way when coming out of defrost. Have you looked at the outdoor unit when it's blowing cold air" If it is getting "stuck" in defrost, the fan won't be running.
BTW, what kind of outdoor temps are you talking about when it does this?
Bob wrote:

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If the reversing valve is getting power during heat cycle, other than during the defrost cycle, it is getting that power from one of three paces: the thermostat, a short in the wiring between the tstat and air handler or the air handler and condensing unit, or a faulty defrost board. Anything is possible of course, but I do not recall ever seeing this particular problem with a thermostat or defrost control. Disconnect the orange wire from the thermostat and if the problem continues, it is not the thermostat. Then disconnect the O wire at the condensing unit. If the problem continues, it would indicate the defrost board. If not, the wiring. Good luck Larry
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It sounds like either a sticking reversing valve or a weak coil. It might also be incorrect refrigerant charge.

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In alt.home.repair, you wrote:

Thanks!. This is exactly the information that I was looking for.
* I disconnected the orange wire from the thermostat and turned on the heat pump. * It put out good heat and the voltage at the disconnected orange wire was 26V. * About ten minutes later, I heard the swooshing sound of the reversing valve and the unit began to blow cold. The voltage at the disconnected orange wire at the thermostat read 0V. * The heat pump continued to blow very cold continiously (longer than 30 minutes) and I climbed on the roof and checked the unit. The external fan *is* running. * I'll see if I can figure out where the oragne wire at the condensing unit is.
Thanks, -Ben
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Gotcha...

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The next time you get plonked.

I'd
sometimes
board
no
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Me??
You got to admit: You weren't very clear on that first post.....

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The OP talks about voltage on the wire to the reversing valve changing when the unit is blowing cold air vs warm. I assume he is checking from Red to Orange, as he says it is 24+ when the unit is heating an 0 when it is blowing cold air. This would iindicate that the valve is getting power and is most likely OK--luckily, since replacing a reversing valve is no small job. No matter what is powering the valve when it is not supposed to be,it is going to be minor compared to replacing the valve. Larry
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Thats a nice crystal ball you have there "BooBy". Too bad you are wrong on this one. Keep up the bad work though. You pretty decent for a little entertainment for now. By the way.......how does that theory work when you have a heat pump that puts out 99 degrees? (I cant wait to hear this one) Bubba

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snipped-for-privacy@qwest.net wrote:

Also in AZ.
About 15 years ago I owned a Knoell starter home in Chandler with a Goettl heat pump on the roof. After the heat pump was about 5 or 6 years old, the first time I would try to fire it up in heat mode every year, it would be stuck in AC mode. On that unit, there was a relay in the unit on the roof, controlled by the thermostat, that applied line voltage to the reversing coil. Popping off the cover and whacking the relay with the handle of a screwdriver was enough to break it loose and it would work for the rest of the heating season.
After about 3 years of that nonsense, got tired of the annual trip to the roof and replaced the relay. No problems after that.
Don't know if this has anything to do with your problem, but thought it was worth a mention.
Jerry
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