Frost or ice on the outside of a heat pump compressor

**JIM MURPHY** · 12-01-2011, 05:12 PM

Did an inspection where both heat pumps where loaded with frost on the outside of the units. The units were running at the time. Do heat Pumps go into a defrost mode when this happens. Eventually the ice melted. One of the systems did not preform adequately. Was this the result of that. It was not that cold, in the 40s.

Jim

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**Dom D'Agostino** · 12-01-2011, 05:25 PM

Yes, heat pumps have a defrost cycle. The frost, or ice, on the coil will stop the airflow, so it has to defrost.

Read about Carriers heat pump defrost on page 4 of their manual.

**JIM MURPHY** · 12-01-2011, 05:40 PM

Thanks a lot Dom

Jim

Tom Huling · 12-02-2011, 06:05 AM

Low voltage wiring is incorrect.

Typically, someone other than the HVAC contractor familiar with the particular brand has worked on the units.

Did you notice if new programmable thermostadts were recently installed?

Bob Cone · 12-08-2011, 07:17 AM

The icing would be expected; todays "demand defrost" controls allow more ice to accumulate than previous control strategies. If it was that thick while you were there, then the fact that they both defrosted during your inspection is a good sign.

**Vern Heiler** · 12-08-2011, 10:08 AM

Originally Posted by Tom Huling

Low voltage wiring is incorrect.

Typically, someone other than the HVAC contractor familiar with the particular brand has worked on the units.

Did you notice if new programmable thermostadts were recently installed?

Low voltage wiring nor thermostat are involved in the defrost cycle.

**Matt Fellman** · 12-08-2011, 01:41 PM

While we're on the subject... I've always wondered what causes the built-up on a straight A/C unit? I see it fairly infrequently (usually on the vapor line near the compressor) and write it up but don't know the cause. If I were to guess I'd think something in the system is clogged or not allowing the right flow of freon, etc.

Bob Cone · 12-08-2011, 02:40 PM

Originally Posted by Matt Fellman

While we're on the subject... I've always wondered what causes the built-up on a straight A/C unit? I see it fairly infrequently (usually on the vapor line near the compressor) and write it up but don't know the cause. If I were to guess I'd think something in the system is clogged or not allowing the right flow of freon, etc.

That is a low evaporator loading problem- not a refrigerant charge problem as is often presumed. Look for air flow restrictions and the like. Trust me, there is PLENTY of refrigerant in the system, just not enough heat (warm air) to evaporate it before it gets back to the compressor

**Matt Fellman** · 12-08-2011, 08:02 PM

Originally Posted by Bob Cone

That is a low evaporator loading problem- not a refrigerant charge problem as is often presumed. Look for air flow restrictions and the like. Trust me, there is PLENTY of refrigerant in the system, just not enough heat (warm air) to evaporate it before it gets back to the compressor

Thanks Bob.... that makes sense.