A/C service question for noob a/c tech - http://www.hvacmechanic.com/ Forums
Original message
| northernfitter
 |  "A/C service question for noob a/c tech"
, posted Sun 25 May 16:45  
Posted this on the HVACR page by mistake first sorry for the double posting. Hey all, I just put a 3 ton r22 system in a 5 year old high velocity system. The original a/c in the system was a year old and was hit with a snow plow. I reused the existing coil in the air handler as well as the txv as they are matched with the air handler. I am currently getting 55psi on the low side and 160psi on the high side with the ambient conditions being around 22'C and after running it for a little while you can see the coil start to freeze up. I am not familiar with the high velocity systems and am not sure if this is just a matter of adjusting the TXV. The line set was only about 15ft so as far as I am concerned the factory charge should be enough as far as refrigerant goes. I have 14 years as a natural gas service tech but only a couple years experience doing a/c service any help would be appreciated. thanks
14years as a service tech in Ottawa and the valley. www.reliableheating.ca. For furnace manufacturer ratings go to
http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/gas-furnaces/furnaces-repair-history-205/overview/index.htm?resultPageIndex=1&resultIndex=1&searchTerm=furnace
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Replies:
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| northernfitter
| "Re(1):A/C service question for noob a/c tech" , posted Sun 25 May 17:34
Got an old friend on the phone finally with much more a/c experience than I and it sounds like its actually low charge after all. The super heat was high and both high side and low side pressures low. I never thought to check the sub cooling will have to go back on Monday and be a little more thorough.
14years as a service tech in Ottawa and the valley. www.reliableheating.ca. For furnace manufacturer ratings go to
http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/gas-furnaces/furnaces-repair-history-205/overview/index.htm?resultPageIndex=1&resultIndex=1&searchTerm=furnace
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| | Freon
| "Re(2):A/C service question for noob a/c tech" , posted Mon 26 May 09:24
If the system was working before the snow plow, don't touch the TXV. High superheat means the TXV is wide open and there is still not enough R-22 getting to the coil, as you suspected. You should also notice zero subcooling. As you add R-22, at one point the superheat will drop the the TXV set temp... usually 10 to 15 degrees. Then you should notice the subcooling start to increase. Try for ~10 to 20 degrees subcooling. Of course if the condenser mfg has charging instructions, follow those. All of the above assumes a clean indoor coil and new filter.
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| | dcdraftworks
| "Re(3):A/C service question for noob a/c tech" , posted Mon 26 May 12:05
Fitter,
Duke thinks you're overcharged, so do I. What is the liquid line temperature?
Elmo
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| | northernfitter
| "Re(4):A/C service question for noob a/c tech" , posted Mon 26 May 12:47
I couldnt take the temp on the liquid line because apparantly the o2 sensor on my tpi is fubared so I couldnt get to the temp setup on it. I am going to the supplier today to get a seperate temp set up and send back my 709 for warranty repairs.
14years as a service tech in Ottawa and the valley.
www.reliableheating.ca.
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