Heat Pump Defrost Cycle every 5 minutes


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Old 12-27-07, 10:29 AM
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Heat Pump Defrost Cycle every 5 minutes

My Rheem heat pump cycles into defrost mode after about 5 minutes of being in normal heat mode. It then spends just a few minutes in defrost mode and then goes back into heat mode.
It's one of the defrost systems with the defrost control board and a defrost sensor on the coil.
NOTE: this only seems to happen when the temp is down below 40 or so. Otherwise it never goes into defrost mode.
 
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Old 12-27-07, 11:21 AM
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A few other things:
  1. I'm looking at my schematic and I see that the reset pin of the defrost control board is wired to something off-schematic. The note on the diagram says "to heat pump monitor 2.5VA MAX. when used". Any idea what that is?
  2. I feel like I'm damaging my compressor by having it cycle from heat to cool every 5 minutes. That "whoosh" sounds like the sound of years coming off the compressor life. Should I just stop using the compressor and go to emergency heat until I get this resolved?
  3. Given that I live in Tucson and we're pretty short of cold weather or high humidity, do you see any problem in just disabling the defrost circuit completely?
 
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Old 12-27-07, 06:51 PM
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I am not able to pull any info on Rheem/Ruud equipment, so you'll have to be my "eyes".

On the schematic, did you see an option to set the defrost time?

Do you see a pressure switch or temp probe tied to the defrost board?

How old is the unit?
 
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Old 12-28-07, 08:14 AM
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There's nothing on the schematic, but on the defrost board itself there's a jumper that can be in one of 3 positions. I don't know what the settings are, but I'm assuming it's a 90/60/30 minute check cycle???
There is a "defrost sensor" that's wired in series with the defrost relay coil and the 'O' terminal of the defrost board. The sensor itself is mounted on the coil.

It's an older unit (probably about 20 years old), but the compressor is only about 5 years old.
 
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Old 12-28-07, 10:29 AM
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Is that sensor making good contact on the line? Is the line frosting up fast in that area where the sensor at?
 
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Old 12-28-07, 01:07 PM
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I'll check that. I don't think it's really icing up there. At the worst it might get a little frosty, but not anything like the "blocks of ice" that other people talk about.
However, it seems to me that the defrost control shouldn't allow the defrost cycle to come on more than once every 90 minutes, regardless of the state of the sensor?? No??
 
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Old 12-28-07, 01:38 PM
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Wink

You sure the charge is ok on the unit??????
 
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Old 12-28-07, 03:08 PM
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I don't really know. Acutally I don't really know how to check. I've got a manifold gauge set that I use when servicing automotive A/C, but I've never tried hooking it up to my heat pump, nor do I even know if that's somthing that is possible. For that matter I wouldn't even know what a good charge would read out at. I suppose I'll browse around the Internet for some information about this
 
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Old 12-28-07, 03:50 PM
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That what I was asking about the frost pattern, it may be low on charge, and the sensor is getting the frost quickly...

I would not advise you to put the gauges on, may be best to call the pro... My guts are saying it's low, and the sensor is getting a "false" reading.
 
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Old 12-29-07, 08:50 AM
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OK, I've got an update. As for the frost pattern, it appears that a light dusting of frost accumulates on the tube loop backs of all the coils, but it disappears before the tubes reach the fins. The frost pattern looks consistent on all the coils from top to bottom. Don't know if this helps at all..

However, another quite frustrating development has occured. I was messing around in the electrical box yesterday and today it appears that the problem has gone away. The only substantive thing I did was move the time jumper on the defrost circuit to another position, but I did wiggle a bunch of wires. The temperature and humidity appear to be similar to previous days when I had the problem. Ughhh. I know the problem will come back and now it's going to be much harder to diagnose... Oh yeah, also the fuse on my aux circuit blew, but I can't imagine that that could cause this problem...
 
 

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