How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7542
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

3 yr old goodman heat pump. Only 1 degree delta at register.

Resolved Question:

3 yr old goodman heat pump. Only 1 degree delta at register. Outside temp 40 deg. suction line (large line) 146 deg (mnfg spec for hotgas method 110+/- 4 above outdoor, so this looks fine). Liquid line appx 70 deg. Pressure on both lines 200psi (mnfg spec around 300 for large line). Defrost cycle works. reversing valve seems to cycle fine. Temp across indoor TXV 110 deg on both sides. Did notice some frost on outdoor TXV capillaries. Cheked return ducts all good and measured delta temp right at air handler only 1 to 2 deg. Unit seemed to work fine last year and all summer. Runs all night. I missed something the unit did have low cooling this past summer and took about 1.5 lb of 410a. It was dialed in to exact mfg performance specs and worked fine all summer 7deg SH and 7 deg SC with 6 amps on compressor. It was thouroughly leak checked and nothing found. Commpression fittings on txv were checked for tightness since it was a potential place to leak but nothing found.
Submitted: 4 years ago.
Category: HVAC
Expert:  Phil replied 4 years ago.
All work to be done by licensed professional. WE KEEP GOING UNTIL YOU HAVE THE INFORMATION YOU NEED, I come and go. This is step ONE.

Hello, so far it sounds like it has a refrigerant leak and is about 50% low on refrigerant... that will produce a 1-4 delta T... depending on other factors.

If the capillaries on the outside unit are frosting, and just the first few inches of the coil were each is attached is frosting...then the system is quite low on refrigerant... the leak needs to be found and repaired... then the system recharged.

Look that over and tell me if you see that situation on your end or not, we can go from there until this resolves.


Phil and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.
Yes Phil, That is exactly what i see on the outside unit just a few inches where capillaries attach and the top of the txv frost up. I have a leak detector and snoop and have been all over this unit and can find nothing. I have also checked for signs of oil or a leak at all joints. Do you have any suggestions to find the leak. I am guessing it is in the A coil. I am certain it is not anywher wher I brazed since I was meticulous and throughly leak checked my work multiple times.
Expert:  Phil replied 4 years ago.
Hello again, I was not notified of your response..sorry about the delay..if that happens again, press the matter.

You sound well qualified to check leaks .. it is a leak though as you know, unless its been this way from the start.

checking for signs of oil is prime clue on tiny leaks, unless the leak is at the top of the joint, then very little or no oil will show.

Goodman coils are know for using the thinner copper tube and have been prone to leaks, Goodman has never been bad about replacing them.

You may end up having to pull the coil to check it.

Thanks for accepting, follow up can go on as needed on the same dime

Customer: replied 4 years ago.
Phil, Found leak at evap coil. So small that my sniffer would barely detect them but noticed oil in the fins. Decided to try A/C super seal and it seems to be holding charge. I do have a question. In heat pump mode I can only get about 20Deg delta and the spec manual says 26Deg+/-3 at 45 outside and 70 inside. I have the pressures right about where they should be at 100 and 300psi. Airflow is at 850cfm. ducts all tight and both coils clean. Do you have any suggestions. I have charged it by pressure since it has been too cold for me to charge it in A/C mode. I am only familiar with using the SC/SH to charge in A/C mode.
Expert:  Phil replied 4 years ago.
Hello again, a lot of the guys are using the Testo 550 instrument to charge systems with, especially heat pumps. see this video

Super heat and sub cooling in the 6 degree range should do it for the system you have. If the delta T on the indoor coil it still a little low the cause is likely more air flow than the system is rated for in heat mode.... combined with inevitable1 to 3 inaccuracy of the thermometers you are using.

If your sub cooling is much over 6 degrees on the indoor coil, under the conditions you describe, the system is likely over charged by a few ounces....

My experience has been that its best to check the refrigerant charge again in the summer, it seems to be easy to get a slight over charge in heat pumps in the winter... then in the summer that runs the suction pressure up high enough to ruin the system efficiency and run the electric bill up noticeably. (because humidity/ latent heat loads are an issue in the summer, but not in the winter to the same degree.)

I would not charge the system to the air flow delta T across the coils, but only by super heat/ sub cooling... on both the inside and outside coils under the conditions you describe.

good luck with that sealant. Goodman coils are well known for leaks. They use thinner copper in the coils than some other mfgrs. You may want to look into a warranty replacement.. at 3 years its likely out of warranty, but Goodman has been pretty good about replacing leaking coils... it would be worth a try. if the leak is where the tube expands into the galvanized tube sheet, its cracked...and will get worse over time.


Customer: replied 4 years ago.
Thanks. I will wait till warmer weather and check the SC / SH. For now I have a good amount of heat and system pressures are right on. The leak was exactly as you atated in the coil fin area and not at the outer u tubes. I will get a coil quote and be preparred if it continues to leak. thanks.
Expert:  Phil replied 4 years ago.
Thanks for the feed back, it will be interesting to see how long that sealant lasts in any case and if it interferes with refrigerant metering or the 4 way valve.


Related HVAC Questions