Heat pump knocking

[Znobyrd]

16 SEER R-410A Goodman, with scroll compressor, owned for 9 months, has been building up a rather nasty sounding knocking noise for a couple months now whenever the condenser shuts off. It's loud enough to hear from inside the house quite well, and is a "winding-down" kind of knock, knocking 6 or 8 knocks, getting quieter as it ends. The whole thing lasts maybe 1 second. Without taking it apart, it sounds like it's coming from the compressor, but not 100% sure. Can this be a sign of a failing compressor or refrigerant problem?

[karsthuntr]

It must be the install guys helper knocking. He is probably pretty hungry if hes been in there for 9 months. :D

It may be the comp knocking, get you installer back out and look at it.

[rponson]

If it that new it should be in warranty. What does the installing contractor say

[coolmen]

time for service

[docholiday]

can I guess?

The lineset is in the wall.

[RoBoTeq]

can I guess?

The lineset is in the wall.
You thinking refrigerant equalization causing the tubing to move? I would also look for this.

You can get some pretty strange sounds from refrigerant systems. Sometimes it is quite difficult to pinpoint where the sound is originating from and even more difficult figuring how to stop it.

What are the model numbers of the outdoor unit and the indoor unit? The outdoor unit will be a SSZ16*** and the indoor unit should be an AEPF****

Also need to know if a txv was installed where the small refrigerant line enters the air handler. It will be an insulated device with copper lines running from it to a sensing bulb connected to the large refrigerant line and another that is directly connected into the large refrigerant line.

Please tell us that this system was professionally installed. (and truthfully, not just because I asked you to :D)

[Znobyrd]

Condenser: SSZ160241, (2 ton) on ultralite pad, 6" pump up.
Air Handler: AEPF303616, (recommended 3 ton for the 16 SEER condenser, dipswitches set for 1200 cfm, the lowest cfm).
10K electric backup in A/H.
T-stat: Honeywell Vision Pro 8000 3ht/2 cool.
No other accessories

The lineset IS inside the wall. 7/8" dia. suction line, 3/8" dia. liquid line, 28 total feet of suction line, 26 total feet of liquid line. I'm aware the suction line is a bit larger than necessary, a 3/4" size is recommended, but was told this wouldn't be a problem. It runs 5 ft. from the condenser, along the wall horizontally , turns into the wall, goes vertically 8 ft up the outside wall (inside the wall) of the house, then runs about 11 ft horizontally on the floor of the attic to the A/H, which is hung about 5" above the floor on threaded rod/unistrut. Both lines then run up the side of the A/H to where they enter the A/H about 2" down from the top of the A/H. At that point the large suction line does an inverted loop so it's about 3" above the coil. The small liq. line goes straight up to the TXV and enters the A/H.

The TXV is installed where the small liq. line enters the A/H. The TX bulb is secured tight at the 10 o'clock position on the suction line; but something here bothers me. The liquid line is touching the wrapping of the TX bulb. This might create a temperature mis-management at the bulb. I could move the bulb over to the 2 o'clock position, or try to bend the liquid line... but not a good idea, it could crimp or blow the line.

As for it being installed professionally, you decide. I installed it, am a mechanical engineer (woo-hoo), with alot of commercial, and fair bit of residential heating & cooling experience and field work, but no EPA license, so I wanted to do my own install. I consulted with an hvac professional the whole way through the install, even on the smallest details, and of course read all the install and setup materials. Then had it inspected by him and was told it was a very good install. He made no changes, we pressure tested the lineset, did 3 evacuations and broke in between each with nitrogen, then weighed out and topped off the R410A with 12 3/4 ounces due to the added line set length, and programmed the t-stat. It started and ran flawlessly for several months... and then came the knocking.

I just did some math, there would be an overcharge of more than 6 ounces of R410A, if Goodman puts in enough for 15 ft. of lineset, and there is an additional 11 ft. of liquid line (.6 ounces additional R410A for every additional foot of liquid line would need to be be 11 x .6 = 6.6 additional ounces, not the 12 3/4 that was added)... but the suction line is oversized, is this still an overcharge?

I opened up the condenser unit today, cleaned it out, carefully moved a couple lines that might knock together, and listened as it shut down, sounded like inside the compressor knocking to me.

Thanks for all the suggestions and council.

[gary_g]

As for it being installed professionally, you decide. I installed it, am a mechanical engineer (woo-hoo), with alot of commercial, and fair bit of residential heating & cooling experience and field work, but no EPA license, so I wanted to do my own install.

Here comes all the "No DIY help offerred on this site" reply posts.

Did you measure and calculate superheat and subcooling per the Goodman installation manual for a TXV-equipped system? Refrigerant charge is based on sub-cooling for a TXV system. Sounds like you added charge based solely on the length on the lineset and not on subcooling.

Best to you.

[everythingair]

You would be correct Gary. It appears that the poster needs to have a qualified HVAC technician do a very careful diagnosis of his system at this point.

There are several wrong things that have been done by the poster and he doesn't seem to fully understand all of the nuances of the installation process. My initial guess from what I am reading is that the system is indeed overcharged (and maybe not by just a small amount) and that the continued use of an overcharged system may have caused compressor damage (professional speculation).

Without superheat and subcooling numbers there is no way to even begin to determine what could be going on with this system. The 1200 cfm of air is certainly not the best condtion. That is creating 50% more air then the system should be running at. For cooling, that is a 50% more load condition.

Sounds like a matter of someone not fully understanding of what he is doing just making what he has installed look like the pictures in the installation manual. After all, a great looking steak doesn't need to taste all that good if the cook just didn't understand what he or she was doing during the preparation.

[Znobyrd]

1200 cfm is supposed to be right for this system, the specs say to set it at 1200 cfm for the 2 ton condenser. When mating the new Goodman 16 SEER, 2ton condenser (much larger coil) to the air handler, the air handler is supposed to be the 3 ton model, and set as per the the 3 ton model. Goodman says so, the hvac guy, the equipment vendor, and the manual all say so.

You are correct about not understanding all the nuances of heat pumps, hope I don't destroy my system before I do.

The hvac pro didn't take superheat or subcooling temps to determine the added refrigerant, just went by length of lineset.

Sounds like I better get the temps done and determine if there has been damage to the compressor. Feel free to point out any more errors you might have picked up on, I plan on keeping this system if possible.

[jrbenny]

<snip>I installed it <snip>
Enough said.

Thread closed.