Questions Regarding HP Sizing And More
Hi Guys, I went out to a no heat/heat pump service call yesterday. Found a bad compressor (breaker shutting off, no continuity). I came back today to replace the compressor/run cap/dryer. I pulled a 400 micron vac, weighed the charge in and fired it up only to get a 12* temp rise. I checked the air flow settings and noticed it was set for 4 tons of air for a 3 ton ODU. I set the airflow correctly and was able to get to a 15* rise... This got me going through things with a fine tooth comb. I found that the house had a lot of ductwork (60-70 actual, not equivalent, feet of duct to supply the lower level. 50 actual feet for the upper level. Upper level is 8x20 as far as I can see, lower starts out at 8x20 then goes to 16" round in the crawlspace). There are (9) 4x10x6 supplies, (8) 3x14x6 supplies, and (2) 2 1/4x10 toe kicks. I'm no Einstein but this certainly seems like more duct than 3 tons of air can handle. After setting airflow to 3 tons the flow from the registers was piss-poor. I also noticed all the windows in the house, tons of them. I decided to do a heat loss tonight. Results:
Heat Loss 45,876
Heat Gain 38,566
@ Design Conditions-35* ODT/72* IDT
Here is some info from the heat pump/coil. I realize I should have checked evap superheat but didn't. Also, there was no True Suction port on the POS heat pump.
HP American Standard 4A6H4036B1000AA
ODT - 52*
IDT - 62*
Temp Rise - 15*
Liquid line temp at coil - 72*
Suction line temp at coil - 118*
High side PSI - 216
Low Side PSI - ?
The main reason for this drawn out post is to get your feedback on the exact cause of such a low temp rise as well as a possible causes for compressor failure. It sure feels like we are going to replace this 5 year old unit with a 4 ton provided the air handler is adequate, which at a glance I think it is. Also, do you think the stock TXV in this air handler is the correct one for a 3 ton unit? The installing contractor really screwed the pooch on this one but I just wanted to hear your thoughts. I think they sized the HP based on the gain instead of the loss and also paid 0 attention to the duct. Whattaya think?
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