heat pump iced over


  #1  
Old 01-07-06, 09:42 AM
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heat pump iced over

Got up this morning... heat pump coils were completely covered in ice.
This is the 2cd time it has happened, and both times it has been below freezing during the night.

Works fine in both heat and a/c modes otherwise.

What should I be looking at that is causing it to ice over when it's below freezing?

I don't know whether it is going into defrost or not (haven't had the time to sit and watch it). The fact that it is icing over tells me no, but it only doing when it's really cold makes me wonder.
 
  #2  
Old 01-07-06, 01:30 PM
jhig1961
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sounds like a bad defrost board or sensor, if you open the condenser cover there is a curcuit board (don't know what brand you have) on the board there is a place to force defrost 2 pins it might say speed up of def, something like that. with the hp running in heat use a screw driver and jump accross the pins this should force defrost,it might take several seconds of holding the screw driver on pins. If it does not go into defrost the board is most likly bad. If it does go into defrost there is a jumper wire for differant time settings move it to the lowest setting.
 
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Old 01-07-06, 07:22 PM
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The board is new, and the jumper is set for 30 minutes.

A little back history..

About 6 months ago, it got hit by lightning, I replaced the defrost board but it'd kick in to defrost with the AC on (and light up the heat strips).
Tech replaced the thermostat wiring run, still ran defrost in AC mode. He replaced the defrost board (again). Still ran defrost in AC.
Said there was some sensor, he would cut the wire to, if that fixed it, he'd replace the sensor. It seemed to, I called and let him know, I can only assume that he replaced it.


Last night was the 2cd time this winter the temps have dropped below freezing (it was 17 here last night).

If I had the money, I'd replace the whole unit with something better than a 10 seer, but right now, I can't.

I do remember seeing the test procedure for testing defrost, I'll do that tomorrow if I need to turn the heat on. Haven't needed to run it all day, and it ran less than 90 minutes betweem midnight and about 8am, been 72 inside all day.
 
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Old 01-26-06, 09:44 AM
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Just thought I would post an update.

Finally got cold enough long enough for me to check the defrost using the jumpers.

It worked.

The only thing I can think of is that I didn't get all the wires tying the heat strips to the rest of the system moved around. I had the breaker for the heat strips turned off, but I turned it on for the test.

A quick look at the wiring diagram leads me to believe that the wire that tells the system to count running time and thus go into defrost at the selected interval is not powered with that breaker off. When it warms up again I will have to take the rest of the cover off and get a closer look.
 
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Old 02-13-06, 03:13 PM
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Finally got a chance to look at this again..

The wire to the defrost sensor was cut. I wired it back together. Still no luck on getting it to go in to defrost on it's own.

According the the diagram, if you short T2 to DFT, and then touch TEST and C together (for 5/10/15 seconds, depending on if the delay is 30/60/90 minutes), it should go in to defrost (it does) and stay there until the defrost sensor reached 68 degrees, 10 minutes have passed, or T2 and DFT are disconnected. It also says if you leave T2 and DFT shorted together, defrost will be completely disabled.

On a hunch, I ran continuity on T2 and DFT and sure enough, they are shorted together _without_ the jumper wire installed. According to the diagram, that has disabled automatic defrost.

But why would these be shorted together?
Keep in mind this is a new control board, the _second_ new control board.

The defrost sensor is suppose to "open at 68 and close at 32". It was probably mid 50's when I did my check, and it too had continuity.

So what, I have (another) bad control board AND a bad defrost sensor?
 
  #6  
Old 02-14-06, 05:48 AM
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Now I am really confused..

Defrost is working now,, heat strips aren't.

Any heat I get while it's running, I lose during the time it's in defrost!
 
 

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