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Old 12-31-2008, 11:56 AM   #1
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2007 Presidio 39D. Have two Dometic 620525 units. 13,500 BTU. We just returned from a trip where we did not use roof air but experienced near freezing temps a couple of times. Today, back home in FLA with coach interior at 87 deg, I discovered that neither unit works properly. They both will blow warm air for about a minute and shut down. Compressor does not appear to run. Is this related to the cold temps we experienced?
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Old 12-31-2008, 11:56 AM   #2
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2007 Presidio 39D. Have two Dometic 620525 units. 13,500 BTU. We just returned from a trip where we did not use roof air but experienced near freezing temps a couple of times. Today, back home in FLA with coach interior at 87 deg, I discovered that neither unit works properly. They both will blow warm air for about a minute and shut down. Compressor does not appear to run. Is this related to the cold temps we experienced?
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Old 12-31-2008, 12:31 PM   #3
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I had that same issue (Sunstar 32K 30 amp with an EMS system) and I recycled all of the circuit breakers (including the one on the generator) and it cleared the problem. Didn't make sense and it might have been a different problem but the circuit breaker cycling cleared the issue.
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Old 12-31-2008, 01:52 PM   #4
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Tried shore power, genset. Recycled all breakers. Checked voltage and freqs. All good. I am baffled.
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Old 12-31-2008, 02:30 PM   #5
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Hi Eddie, does the compressor try to start?
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Old 12-31-2008, 03:04 PM   #6
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I can't hear either one trying to start. The only common link I can see is the thermostat. It's a Duo Therm Comfort Control.
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Old 12-31-2008, 03:47 PM   #7
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The Tstat is sending the signal to start the cycle (blower motor is on). The problem seems to be the compressors do not turn on and the blower shuts down.

1. I have a service/installation manual for some heat pump units. PM me with your email address and I'll send it to you. If the manual is for your model, the last page has the wireing diagram. You can check to see where the voltage is being lost.

2. This may be a dumb suggestion, but make sure both units are set for A/C. If not, neither will work on A/C.

3. I know you mentioned you checked this, but double check the shore power. Make sure you have 50 AMPS on each leg of the circuit.

4. Try starting the units via the gen set. See if any symptons change or breakers pop.
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Old 01-01-2009, 06:14 AM   #8
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Thanks for the reply. I agree with the shutdown for no compressor start. As mentioned, I tried on shore power and the genset. Both units are set to cool.

I have a surge /fault protection system that shows proper volts and freqs on both legs.

I have the installation manual that shows a freeze control circuit. I wonder if having been in freezing temps has any bearing here. It's weird that neither unit will cool.

I will go on top in the next day or two and pull the covers to see if there are any breakers, etc under the cover.



<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GaryKD:
The Tstat is sending the signal to start the cycle (blower motor is on). The problem seems to be the compressors do not turn on and the blower shuts down.

1. I have a service/installation manual for some heat pump units. PM me with your email address and I'll send it to you. If the manual is for your model, the last page has the wireing diagram. You can check to see where the voltage is being lost.

2. This may be a dumb suggestion, but make sure both units are set for A/C. If not, neither will work on A/C.

3. I know you mentioned you checked this, but double check the shore power. Make sure you have 50 AMPS on each leg of the circuit.

4. Try starting the units via the gen set. See if any symptons change or breakers pop. </div></BLOCKQUOTE>
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Old 01-01-2009, 09:30 AM   #9
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Eddie,

I know about the freeze control circuit. Me thinks it is for when the units get frost on the coils. The compressor will shut down, for a time, to let the unit defrost itself. The fan will remain running. This is how my units work.

While you have the covers off, consider checking the start & run capacitors for each unit. I know it is a very remote chance both sets went bad, but as long as you have the cover off, what's a couple more screws and one cover.

Will the fan stay on when the Tstat is set to fan only?
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Old 01-01-2009, 12:13 PM   #10
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Now I am really baffled. I reset the thermostat with no luck. I went on the roof and removed the cover on the rear air. There is a 3 amp fuse that was fine. I turned the rear air on and as I suspected, no compressor.

Buttoned the unit back up and came down.

Tried them both again with no luck. Just for grins I thought I would try them on the genset even though I had already. Lo and behold, they both cool. Shut down the genset forcing a switch to shore power and both units shut down.

Turned the thermostat off and back on and both units cool.

This leads one to suspect a power problem. But I have an EMS that monitors for surges, voltage fluctuations, and freq problems. The unit will shut off genset or shorepower if there is a problem. It also displays the volts, freqs, and faults on both legs. Both have been steady on 120v and 60h. The only thing I can think of is that maybe the EMS was not passing full current.

I have my fingers crossed.
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Old 01-01-2009, 02:13 PM   #11
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The transfer switch could also have a problem. For now, if it ain't broke it can't be fixed. Good luck.
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Old 01-02-2009, 05:35 AM   #12
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Eddie,get a can of air like for computer use and blow out both thermostats real good. Dust is a big problem in the motorhome and it takes very little dust in the thermostat to give you problems.

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Old 01-02-2009, 09:08 AM   #13
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Eddie, your transfer switch may have dirty relay contacts. With the power disconnected open cover find relay contacts and run a dollar bill thru contacts could have dirt or pitted contacts that need cleaning on shore line power side.
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Old 01-02-2009, 10:44 AM   #14
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I had Yellow Jackets build a nest on the drum fan under the cover of the A/C unit
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