Carrier Heat Pump Frosting Over - http://www.hvacmechanic.com/ Forums

Original message

hvac novice

70.186.205.133

"Carrier Heat Pump Frosting Over" , posted Tue 22 Jan 21:52

I've got a 2 ton Carrier heat pump that completely ices over.I have put on a new defrost board and the defrost thermostat checked good.The heat works real good,but it freezes up after running for awhile.This is in below 40 degree weather and it has snowed a bit the past couple of days.I jumped - out
the defrost thermostat.It was hard to tell if it went into defrost.For a little while it looked like the ice started melting,but the fan kept running.Is there anything else I can check? Any advice would be greatly appreciated!

Replies:

pbservano

205.188.117.9

"Re(1):Carrier Heat Pump Frosting Over" , posted Sat 26 Jan 20:13:

One way to check your defrost thermostat is to immersed the thermostat to glass of ice (32F). Measuring between two wires connectd to the thermostat should be less than one ohms (which is closed, continuity) uing an ohmmeter.... Also to check to ensure your defrost control board is not at fault, is to jumped the two terminal where the defrost thermostat was connected to and placed the circuit board jumper to 30 minutes cycle ( there are normally three settings 30, 60,90 minutes). Have a timing divice, ( stop watch) at approx waiting for 30 minutes the unit should go on defrost mode energizing the reversing coil and de-energizing the compressor blower fan, the compressor (will stay energize) will continue to run. You will notice a loud hissing sound and sometime a steam coming from the unit if there is enough ice accumulated at the outdoor coil. I would also suggest to remove excess ice accumulation if there is any by using a water hose ( the temp from municipal water is normally above freezing point). When the unit goes to defrost mode about 8 minutes or so ensure to remove the jumper to return the unit to normal operation. This procedure is for testing purposes only.... The head pressure can rise pass 300-400 psi, this is not good for your compressor to operate this way.
If above mention does not occur most likely you have a bad defrost control board.

The defrost thermostat should measure closed (less than one ohm) when temperature falls below 30F and opens @ 65-80F. During defrost when the thermostat senses 65F it will stop the defrost cycle returning the system to normal operation.

US NAVY RETIRED

[this message was edited by pbservano on Sat 26 Jan 20:20]

bigglenn357

68.239.71.74

"Re(1):Carrier Heat Pump Frosting Over" , posted Thu 24 Jan 06:33

The wires coming out of your defrost board problably go to a multi purpose relay,make sure that it energizes when going into defrost,could just be a bad relay

Big Glenn
"Imagination is more important than knowledge" (Albert Einstien)

mgussler614

75.180.43.90

"Re(1):Carrier Heat Pump Frosting Over" , posted Wed 23 Jan 21:14

check the charge in the unit if it is low the heat pump will frost over more

guz 1