Bryant 540AJ024 Heat Pump

[jhc]

Old Bryant split heat pump system.  Works great always has.  Now it's frosting up completely on the fins and coils.  I'm suspecting the defroster is whacked.  Any idea if it would be the defrost board, or just the defrost sensor?  How would I find out which one is bad, or both?  Also, what part numbers do I need?  Thanks!

Here's a link to the .pdf manual for it.

http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/pds540a.18.2b.pdf

[ACtechGUY]

Not sure about the part numbers but I do know that if the defrost temp sensor fails the control board will default to a time based defrost cycle( 30, 60 or 90 minutes) .Take a close look at the board. On These older systems they used a wire jumper from the board to a pin to chose the defrost time. check to see if it didn't come loose. If everything looks ok then it may very well be a flaky board.

However the sales papers say that a defrost is not initiated unless frost is sensed( coil temp below 32 degrees). so maybe it is the sensor. take a ohm reading of the sensor to see if it is shorted or open. If you get a good ohm reading let us know the reading and temperature and I am sure someone here will find the resistance to temperature chart for your thermister.