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outside unit won't turn on (miller heat pump)

Posted by monzamess (My Page) on
Thu, Feb 15, 07 at 20:09

Hi all. I have a 10-year-old Miller by Nordyne 3.5ton heat pump with electric auxilary heat. The outside unit will not turn on.

I keep the thermostat set at 68. It has a swing of 3 so the temp drops to 65 (because the outside unit isn't doing anything) and the aux heat comes on just to keep the temp at 65, costing us a ton of money.

On the outside unit, if I push in the contactor by hand, the outside compressor and fan WILL turn on, so I don't think it's something as simple as a breaker.

I have verified that the Y terminal on the outside unit is getting 24V when it's supposed to be on, so I think the thermostat is OK. Also, if I just jump Y to Rh to force 24V on Y, bypassing the t-stat, nothing happens on the outside unit.

I turned the unit to cooling mode and dropped the thermostat to 35 degrees--the outside unit still did not come on.

I am seeing about 5V at the contactor coil...??? Maybe I'm not measuring that right.

I have a Rite-temp digital t-stat model 8050C (OK for heat pumps) that I installed several months ago. When I installed it, I verified that it cooled and heated. I used it most of the summer and it controlled the A/C well and controlled the heat well as we entered fall.

Anyway, I had a pro come out and look at it.

He said my thermostat was junk and not meant for heat pumps and wanted to sell me a non-programmable unit for $249. I explained that while my Rite-temp t-stat may indeed be a piece of junk, and I didn't think it was the problem, explaining what I wrote above.

Then he said he'd replace my contactor for $185 (it's a 621661 that retails for will under $20 as far as I can tell) but would not guarantee that the contactor OR the new t-stat would fix anything.

The tech said the outside defrost board was good but I don't know how he came to that conclusion.

For $75, his final diagnosis was that since I did not connect E to anything on the t-stat, and since I jumped W to Y, I did it wrong and that was the reason nothing was working.

When I installed the t-stat I followed the installation instructions carefully. I even double-checked things online, like why am I being told to jump things together and not connect E to anything. As I understand it, this is OK because E is for emergency heat, which is just the aux heat without the outside unit working, and the t-stat can do the same thing by turning on W2 and turning off Y. I even tried to explain this to him but he thought I was full of you-know-what.

Sorry for my little rant there, I just wanted to drive home the point that I don't think the t-stat is bad, and that I've consulted a pro, and still don't have a running outside unit.

Any ideas???

Thanks in advance.


Follow-Up Postings:

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RE: outside unit won't turn on (miller heat pump)

why did you jumper W to Y?
doing this will make the aux heat strips and condenser run at the same time. in cooling mode this will run heat and cool together effectively running up your electric bill.

did you set up the heat pump/normal and gas/electric jumpers right on the thermostat?

are you sure youre only getting 5 volts across the coil on the contactor? (meter leads on both coil terminals)if this true and you have 24v coming into the unit at the terminals id guess you have a shorted control wire, a bad board (if it has one) or a tripped safety (high or low pressure) switch somewhere in it.

if you have 24 volts at the contactor coil, replace the contactor. around here contactors cost around 7 bucks.
id call a different tech.


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RE: outside unit won't turn on (miller heat pump)

I jumpered W to Y because the t-stat instruction manual said to. Also, according to the site http://www.hvacmechanic.com/tstatwiring.htm Y is 1st stage heating on a heat pump, and W is first stage heating and may require a jumper to Y on a heat pump.

We didn't have any problem with cooling bills or anything back when we needed cooling.

As for safety switches, that's what I was hoping the tech would look at.


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RE: outside unit won't turn on (miller heat pump)

I looked up your wiring diagram and it appears y and w need to be jumpered. im assuming this is because Y doesnt serve as first stage heat in heat pump mode like 99% of other thermostats do. im also assuming w isnt wired to the aux heat and only W2 is wired to aux heat.

normally on a heat pump stat Y is used to engergize the contactor in both heating and cooling modes and the O terminal switches the reversing valve accordingly.

i..e.. in cooling mode Y energizes bringing on the unit with O energized to switch the reversing valve to provide refrigerant flow for cooling.

in heating mode Y energizes bringing on the unit with O de-energized to provide reverse refigerant flow for heating.

your stat does need the jumper in order for W to bring on the unit in heating mode with W2 providing the signal for aux heat. the stats i usually work with have a W/W2 terminal that serves as first stage heat OR second stage depending on setup configuration or dip switch settings.

im assuming W is only jumpered at the stat and isnt connected to the aux heat. if so this could work.
I normally work with honeywell or totaline stats which are congfigurable without the need for jumpers.
your stat is kind of a cheapo but if it serves its purpose more power to ya hehe.

I'd (if i were you) call a different tech out and ask him to look at tracing the safeties.
I would try to explain how to trace the control circuits but that task is best left to a qualified professional.

good luck

Here is a link that might be useful: Ritetemp 8050C stat wiring


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RE: outside unit won't turn on (miller heat pump)

If I apply 24V across the contactor coil, should it activate? Because when I do that it just clicks once like it's trying but failing.


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