View Full Version : Heat Pump defrost problem

04-01-2013, 06:46 PM
Hi everyone – I’m new to the forum – My name is Lon and I am a power engineer working for WhistlerBlackcomb ski resort. I have referred to your site from time to time and found it very helpful. We do as much work as we can on our 300 or so fridges we have in our staff housing complex but the question/what I need help with is for a heat pump. Some of our local contractors are good with air but not so much heat pumps. This unit is a carrier 38YKC 3.5 T R22 with a Copland scroll compressor. This unit will not defrost or go into air cond. – The unit will heat – the 7/8” inlet line at the furnace will run 120 deg + during heat mode (only checked with a infrared therm). The defrost timer works, the reversing valve switches with the audible whoosh and the 3/8” feed line to the TXV at the furnace gets cold but no cold exiting the furnace – the compressor output to the reversing valve is hot but no flow to the outside coil to defrost the unit. It seems to flow only one direction – heat mode. The TXV is a bi-directional Sporlan with the internal check valve. According to the schematic I have on it the check valve closes during cooling mode so everything passes thru the valve itself. It has an external equalizer tube and the cap. tube is attached to the 7/8” line. The question I have is, does it sound like the TXV is screwed up or even plugged? or could it still be the reversing valve even though it seems to be switching. I’ve exposed the bulb on the cap. tube and warmed it up but no better…looking for some expert advice - Thanks

07-01-2013, 06:02 PM
Give the Rev valve a controlled hit with a wooden mallet or use a piece of 2"x"2 and hit that. ;)

Rev valves can stick with age and this can release them temporarily which A) Proves a point, and B) Gives you time to get it swapped out.

Don't smack it too hard or you could fracture your piping! :eek:

07-01-2013, 07:31 PM
When you touch the pipes coming out of the reversing valve, the single one on the top is always hot and the middle one on the bottom is always cold. The pipes either side of the bottom one are either hot or cold, depending on the operating mode.
Touch one of the outside pipes and see if it changes from hot/cold, cold/hot, when you change mode (heating/cooling). If it does, then your RV is working OK and the fault lies elsewhere in the circuit

07-01-2013, 10:20 PM
..............or do it the scientific way as above! :D