Original message
| rgriffice
 |  "Heat pump ODU won't start on its own..."
, posted Mon 25 Aug 21:23  
I'm trying to diagnose or at least understand why my heat pump outdoor unit won't start. I removed the panel of the ODU to see if anything looks amiss (the unit quit working last night while I was asleep). The indoor blower continues to run but nothing from the ODU. A voltage tester confirmed that all components are getting power. I next depressed the contact and the unit started up (both fan and compressor). I held it for a short while and went to check the results inside. The house was about 10 degrees warmer -- the unit was generating heat rather than cooling.
Any ideas what might be the problem? BTW, when I depressed the contact I put my hand on the compressor and felt the chilled refrigerant (at least briefly) but it turned lukewarm as the unit ran.
Thanks in advance for your advice!
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Replies:
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| sinead26ohara
| "Re(1):Heat pump ODU won't start on its own..." , posted Wed 3 Sep 20:51
It sounds like the problem is with the low voltage at the OD unit. I'm guessing there is an issue with the control board since you can manually depress the contactor and get a result. The unit is heating your home when you do this because the reversing valve is only energized on a call for cooling through the board. When you manually depess the contactors the RV does not have a call for cooling placed on it, therefore you are operating in the heating mode. With the stat calling for cooling I would meter the incoming 24 to 27 VAC to the outdoor board (between the red lead and ground). If there is no power going to the board you have a problem between the air-handler and the OD unit. If you have power there, still on the OD board, meter to see if you have 24 to 27 VAC between the outgoing leads to the contactor and reversing valve and ground (they should be the yellow and orange leads, but check your schematic to be certain). If there is no power on these leads the board is faulty. This is a suggestion based on your description of the symptoms. If you are uncomfortable with going any further you should call a qualified service company. Good luck.
Sinead O'Hara
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| rgriffice
| "Re(1):Heat pump ODU won't start on its own..." , posted Tue 26 Aug 13:07
Problem solved...condensate drain line for attic-installed IDU was clogged and pan filled up triggering cut-off switch. One last question: the condensate drain terminates into my bathroom lavatory drain. Does this meet code? The PVC drain from the attic is connected to a brass lavatory tail pipe using a rubber hose with clamps. The rubber hose seems to be bonded to the brass after 10 years; I tried wrestling it off but quit in fear of breaking the PVC fitting inside the wall. I ended up blowing the debris in the line (with my mouth) at the air inlet near the IDU but it seems like a poor design not to be able to easily check whether condensate is draining properly.
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