Resolved Dometic Heat Pump - what's the loud grinding noise?

[TJ&LadyDi]

Heated floors are nice and quiet! Just sayin’.

TJ

 

[Neal]

It seems this "grinding noise" which per above sounds like the defrost, only occurs with temps under about 47F outside. Currently it's 55 out and the heat pump is working well, no annoying noises. Only the bedroom (aft) unit has done this, the other zone has not.

 

[Neal]

Scratch that, it's doing it again. It's a harmonic vibration somewhere in the unit. I could probably go on the roof and push on things to find it but I'll pass on that for now.

 

[Neal]

I've continued to use the heat pump and for whatever reason "that noise" has stopped. For the longest time I preferred the furnace but the heat pump is what I've been using lately and prefer now. It seems to be more effective in heating than the furnace and without "that noise" it's actually less annoying. It's the same sound when using the air conditioner. Even down near 40 last night it worked well.

 

[Neal]

Back to this thread on the heinous grinding noise which is happening in 100 degree weather and trying to run A/C. I did another google and got good results showing freon line vibration. Today I got up on the roof while the A/C was running and sure enough I could see right away the cause. It's a cold line so I could touch it but I used my screwdriver initially and the noise stopped. I wasn't sure how to really resolve this so I had 15 inch cable ties and was able to get the tie through a piece of the casing and pull against the freon lines to keep them from vibrating. I can only imagine the freon line vibration would lead to eventual failure. The cause is probably the blower fan out of whack for some reason but for now we have peace and quiet again. So much so I can't even hear it running. Part of that is because I'm deaf from the high dB noise I've had to deal with all day long from this issue!!!

The freon tube is rapidly vibrating but I think the 30 frames per second video makes it look like its wobbling which it is not. It's a high rate vibration.

 

[Rich W.]

Maybe thats why my rear AC failed on the last trip. The guys at National RV Refer said the compressor was running but it had no charge. Since 99.9999999% of techs wont work on these units and the few that will wont warranty their work, I opted for a new one ($1750 installed). But I brought the old one home and Im determined to either make it work so I have a complete spare, or part it out for the other high failure rate parts.

 

[Buly]

Neal,
Oscillation like that may break the copper lines, and you will have an expensive problem.
Secure the best you can and look at the other AC’s and fix if needed.

 

[Neal]

The question is where is the root cause of this oscillation? It appears the blower fan is not aligned or something so it's generating the oscillation, but why? How did it get out of alignment? I'll have to go up and check into that further another time. I realize this A/C is nearing end of life at 5+ years old so I'm not overly worried about it, I expect to have to replace it in the near future (1-2 years at best). But I will see if I can find the cause and resolve that to prolong its life. For now the freon lines are stabilized and the unit is silent again.

 

[AbdRahim]

Hope you are wrong about end of life. I sold my last rig at 5 years, but with the mods I made on the inside the A/C was better than ever. There was a guy at the Service Center, getting his A/C's replaced at 17 years. 5 years is ridiculous. So I hope you get much more use than that.

 

[Neal]

I sure hope to report back in 12 years it's still going.

 

[Gronk]

You probably need to pull the cover and pull the fan motor. Then you can pull the squirrel cage out and see what is going on. I just fixed one yesterday for a guy in the campground I'm in for almost the same symptoms. There was enough dirt built up on the cage it was out of balance. It's actually a pretty simple repair.

 

[Neal]

I pulled the lid yesterday and checked both. In the affected system I ensured everything was secure and it was and I was asking myself how can this thing get out of round. I think you have the answer. It will be 104 today so that ain't happening but cool off tomorrow I'll get up and check it out. Thanks!

 

[Buly]

I found mud dobber nest lumps of dirt in my AC. If one built a nest on the rotating part, it will throw it out on balance.

 

[Neal]

You probably need to pull the cover and pull the fan motor. Then you can pull the squirrel cage out and see what is going on. I just fixed one yesterday for a guy in the campground I'm in for almost the same symptoms. There was enough dirt built up on the cage it was out of balance. It's actually a pretty simple repair.

Inspected and everything is clean. Various components are on anti-vibration shock mounts. Anything out of whack can cause the vibration. All is good now, simple fix and good to find before the high frequency vibration resulted in failure (or insanity).