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Old 02-25-2012, 09:19 PM   #1
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Carrier 38YCC036 heatpump knocking


Our 6 year old carrier 38YCC036 heatpump condenser unit is making a knocking sound just prior to going into defrost mode. It was checked out about a month ago and they said the charge was OK. Weather has been normal to warm for this time of year in the Roanoke, VA area. It sounds like the noise a condenser fan blade would make when hitting something (the fan is moving slowly when the unit is making this noise - not fast like when the compressor is running) but the fan is free and isn't hitting anything. Any ideas?

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Old 02-25-2012, 09:27 PM   #2
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Carrier 38YCC036 heatpump knocking


If the condenser motor is running slow then may have weak run cap.

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Old 02-25-2012, 09:48 PM   #3
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Carrier 38YCC036 heatpump knocking


The condenser fan motor runs fine when the compressor is running. But we've noticed this banging just before it goes into defrost. I thought it might be the compressor but I don't know if compressors make such a banging noise?
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Old 02-26-2012, 04:56 AM   #4
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Carrier 38YCC036 heatpump knocking


While a compressor can make a banging noise. It shouldn't.

What kind of banging noise is it.
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Old 02-26-2012, 08:33 AM   #5
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Carrier 38YCC036 heatpump knocking


Metallic sound, like a condenser fan blade hitting something (but it isn't).
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Old 02-26-2012, 09:32 AM   #6
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Carrier 38YCC036 heatpump knocking


Could be a cracked blade.
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Old 02-26-2012, 04:48 PM   #7
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Carrier 38YCC036 heatpump knocking


if not a cracked blade and you call em back tell them to run it in a defrost cycle, shouldnt take too long to figure it out if you are standing next to it. they should know how to do that, hopefully..


maybe reversing valve bouncin around??? slim i know

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Old 02-26-2012, 08:06 PM   #8
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Carrier 38YCC036 heatpump knocking


Quote:
Originally Posted by sktn77a View Post
The condenser fan motor runs fine when the compressor is running. But we've noticed this banging just before it goes into defrost. I thought it might be the compressor but I don't know if compressors make such a banging noise?
Is the unit building up a lot of ice? If so, are you sure the fan isn't hitting the ice buildup just before the defrost cycle? You may have to change the jumper on the defrost board to select a shorter time between defrost cycles.
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Old 02-26-2012, 09:31 PM   #9
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Carrier 38YCC036 heatpump knocking


Yes, the unit is building up some frost on the coils and the pipes inside but not on the fan or fan motor (or, from what I could see, anything the fan touches). However, I'll look closer next time we're up there (this is a weekend/vacation home).

I wondered about the reversing valve as it happens immediately before going into the defrost cycle (as its going into the defrost cycle?) but I'm not sure how this would work?
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Old 02-26-2012, 09:35 PM   #10
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Carrier 38YCC036 heatpump knocking


If the suction line inside freezing up it maybe Heat TXV
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Old 02-26-2012, 09:37 PM   #11
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Carrier 38YCC036 heatpump knocking


It can be valve stuck in cooling. If you put on A/C mode and carefully go out and remove orange wire you be able hard valve shift
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Old 02-26-2012, 11:09 PM   #12
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Carrier 38YCC036 heatpump knocking


The only reason I threw out reversing valve was once on an old window shaker. The reversing valve solenoid was getting intermittent voltage from a bad controller. It was almost 'chattering' till it stuck. Weird, but that was it.

The suggestion to run it in cool would do or if you have the manual in the unit and are up for a walk thru im sure someone on here could tell you how to jumper the defrost board to test a defrost cycle.. or call the same guys back if you dont want to deal.
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Old 02-28-2012, 09:09 PM   #13
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Carrier 38YCC036 heatpump knocking


Well, next time I'm out there, if it is still making the noise, I'll call the HVAC company again and have them check out the reversing valve. Not going to mess with it myself
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Old 02-29-2012, 07:29 AM   #14
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Carrier 38YCC036 heatpump knocking


In my neighborhood there was a lot of carrier/bryant. When they got some age on them, the defrost board would hang up on them and make a clicking sound..like once every couple of seconds.

My neighborhood sounded like a bunch of crickets from the noise on some cold nights.

(while it was clicking- you could go over and kick the unit and it would finally go into defrost )
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Old 03-04-2012, 06:26 PM   #15
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Carrier 38YCC036 heatpump knocking


Well, we went back up to the house this weekend and the outside condenser unit is still making the clanking noise. While the compressor is working normally in heat mode, there is no noise (and the condenser fan speed is normal). When the noise starts, the fan has slowed down and the banging is the same speed as the fan (as if a blade were hitting something metallic). I see/hear this from the kitchen window. By the time I get outside to the condenser, the fan has stopped and it is in defrost mode (it's a timed defrost, set at 30 min, since we had the icing problem and the defrost board replaced last month).

I give up. Will put in a call to the AC company tomorrow.

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