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Carrier 38YCC036 heatpump knocking

6K views 17 replies 6 participants last post by  sktn77a 
#1 ·
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?
 
#9 ·
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?
 
#12 ·
manual defrost

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.
 
#14 ·
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. :thumbup:

(while it was clicking- you could go over and kick the unit and it would finally go into defrost :no:)
 
#15 ·
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.
 
#16 ·
good luck

Thats got to be annoying to hear that.

Post up what they find out with it.

The fella Beenthere had a interesting one about the fan blade cracked. The only other thing I was thinking was as the fan blade accelerates/decelerates it flexes a little. I know this becuse of course I have never put a condenser fan motor a little too low on the shaft, hahaha.

I did one and it flexed enough to tap on a pinch off tube below as it sped up. pulled the disconnect as fast as my a** could get to it. maybe on the decel it is flexing up and tapping the cage. dunno or maybe a set of wires hanging down. (around here it is the reversing wires tie wrapped to the cage that break in 120 degree heat and fall in)
 
#17 ·
REALLY annoying - especially as it's so cowardly as not to make the noise when I get outside to look at it! :wink:

The blades aren't cracked (checked that). I don't know if they can flex enought to hit the refrigerant pipe (I doubt it as the unit only makes the noise when the fan is going slowly - not enough air resistance to flex them that much) but who knows? Will post the solution if and when it gets fixed (the yokels out there in the mountains only work weekdays, and we only go up there at weekends).

:(
 
#18 ·
Update!

Well, turns out is was the condenser fan motor making that noise. When it starts up and slows down, it makes a metallic clanking noise that goes away when it gets up to speed or stops. The AC guy said the motor is going out and offered to replace it but also said it probably has a year or two left in it yet. I'm holding off in case anything else goes wrong, possibly making a changeout the more effective route.

Thanks to all for your help.

Keith
 
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