Author Topic: 0 Subcooling  (Read 4048 times)

Offline johnt2_2002

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0 Subcooling
« on: May 19, 2009, 05:44:31 PM »
hi, i was working on a lennox hs29-211 R22 ac the other day. Head pressure=135psi suction=57 psi superheat 23f outdoor ambient 71 delta T of 17-19 f however my subcooling was 0f? how is this  possible? amp draw on compressor was 6.6amps. the compressor has failed on one ocassion where it stop but fan motor still running 240v one load side read...any tips would be helpful

Offline Admin

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Re: 0 Subcooling
« Reply #1 on: May 20, 2009, 12:13:30 PM »
A low subcooling usually means you're undercharged.  135psig is a very low head pressure, your compressor amps are low too.  I would expect you to be around 200psig head pressure.  What was the indoor wet bulb reading?  You're suction should be above 60psig or you risk having the indoor coil ice up.

Are you saying the compressor is stopping, but the condenser fan motor continues to run?  Test the capacitor.  It sounds like the HERM side has has fallen outside of the +/- 10% range.  Use a multimeter in the uF (micro farrads) setting.

Seal the service valve caps with leak lock, topup the unit and replace the capacitor if required.  Advise the customer if the leak persists they will need an expensive leak search / pressure test completed before more freon can be added.  I usually recover the freon and cut the system in half.  I put 300psig of nitrogen into the indoor coil, and 300psig into the lineset and outdoor coil.  24hrs later you'll know where the leak is.  In either case it's usually a better option to replace the unit, if it's over 12 years in age.