Help with Defrost Cycle - won't run!

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  #1  
Old 12-30-04, 09:41 PM
eagle007
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Help with Defrost Cycle - won't run!

Hi all,

I have a Lennox HP26-48-7p heat pump in the northeast (I know, i know, not ideal). In August, the AC wouldn't run, called a service tech and after 3 hours, he found a short in the 24 volt relay. That fixed it.

In october, the heat wouldn't run, called a technician, and he found that the defrost and timer control board was broken, so we changed that and the heat started to work again, EXCEPT, the heat pump would NOT defrost itself in cold weather so the outside unit (where the compressor is) will totally ice-up within 12 hours.

Called the tech again and he replaced the defrost sensor. That did nothing and now he is stumped (and so am I) b/c he says the control board and the defrost sensor are the only items that should control whether the unit goes into defrost mode.

Some other information: in colder weather (below freezing) the unit will stay on without shutting itself off even if the temperature inside the house is at the desired thermostat temp (set it to 70, temp goes to 70 and the heat pump will stay on for more than an hour, with aux heat turning on occasionally). The tech says that this is the heat pump trying to go into defrost mode but it is not able to.

Above freezing, the unit runs very well cycling on for about 30 mins, and turning off for almost same time.

HELP!!!! Please, this is so frustrating having to deal with this every day. I can't get a different tech b/c the recent weather around here has cause all the companies that deal with heat pumps to have a 3 week back log.

What is/could be the problem???

Thanks for any help in advance and Happy New Year to all.

EDIT: P.S. I forgot to say: the the freon is all charged up (if you look at the sight glass during non-frosted operation, it looks fine and the tech verified this)
 
  #2  
Old 12-31-04, 03:42 PM
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Please switch over to emergency heat and leave the heat pump off until someone can fix it correctly (maybe someone besides the company you've been using?) With temps below freezing, the heat pump isn't saving much if any money. The behavior you describe is normal for a heat pump running in temps that are too cold for it. The aux heat is actually maintaining the temperature. The thermostat is probably designed to overshoot the setting a bit before shutting everything off. Even slightly above freezing there are times when a heat pump needs to defrost to avoid placing strain on the compressor. This needs to be fixed.

Doug M.
 
  #3  
Old 12-31-04, 04:48 PM
eagle007
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Thanks for the reply, dougm.

What do you think the problem is?
 
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Old 01-01-05, 12:45 PM
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Bad board, bad defrost sensor, bad reversing valve or incorrect hook up. Shouldn't be that hard for a pro. to diagnose.

Doug M.
 
  #5  
Old 01-01-05, 02:27 PM
bigjohn1
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The boards have a test function that can be run in order to check them out. Also, some boards have to have a sensor that is compatible with that board.
 
 

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