subcooling too low

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subcooling too low

Postby coolhandluke » Thu Aug 04, 2011 9:04 pm

I have been doing hvac for about a year now so i still have a lot to learn. The other day i got a call from someone saying their house was hot. He told me that his uncle looked at it and told him that either he had too much refrigerant or a blockage and that it needed to be recovered, vacuumed and recharged. For one, his uncle thought it was an R-22 system for some reason even though it clearly said 410 on the lable . Anyway, the system was way undercharged. It was reading 50 psi on the low side and 325 on the high and it was about 107 degrees that day. It had shut off on them several times when they were looking at it which I'm sure was a low pressure switch. I charged it and was getting my pressures about where they needed to be but I cant get any better than 5 degrees subcooling and a 13 degree delta T. The house cools down good enough in the evenings and mornings but gets really hot in the afternoons. It has been around 108 degrees lately but his house will get up to 88. everything is working properly, both coils clean. I'm not sure what to do. Oh yea, its a txv
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- subcooling too low

Postby coolhandluke » Thu Aug 04, 2011 9:53 pm

The low side was around 130 psi and 45 degrees, the high side was 418 temp 120. The supply air was 65.9 return 78. My pressures did fluctuate some but that seemed to be about where they were
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- subcooling too low

Postby coolhandluke » Fri Aug 05, 2011 12:19 am

Sorry, I gave you bad information. I was just giving you the pressures and their corresponding temps. I had about 50 degree super heat but I figured That was because it was so hot inside the house. My suction line was pretty warm. About 90 degrees
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- subcooling too low

Postby Rsc12 » Wed Aug 10, 2011 12:18 pm

Sounds like your down south some where. How old is the system? Model # Could be undersized for the heat load your getting. or still under charged
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- subcooling too low

Postby nomadpeo » Thu Aug 11, 2011 6:52 am

verify the bulb is strapped tight and well insulated, as mentioned. get the subcooling in the 7 to 10 range, then verify proper superheat. you may want to get past the hot 'pulldown' to get the house cooled down to 80 or so before taking some final readings. if the freon is low and the house very hot, the txv is going to throttle wide open to meet the demand.
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- subcooling too low

Postby nomadpeo » Thu Aug 11, 2011 6:53 am

verify the bulb is strapped tight and well insulated, as mentioned. get the subcooling in the 7 to 10 range, then verify proper superheat. you may want to get past the hot 'pulldown' to get the house cooled down to 80 or so before taking some final readings. if the freon is low and the house very hot, the txv is going to throttle wide open to meet the demand.
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