I have a heat pump that is installed with another so combined they are two five ton HP's. The system is installed with a closed loop. The problem is the 1st HP has blown 5 capacitors in the past year. All the obvious have been verified. New larger transformer by the electric company. A power monitor on the circuits for the geo system. All voltages verified, pressures and temperatures verified. What would cause one heat pump in tandem that are staggered by 2 degree differential, one fails and the other never has a problem.

There are a few ways to kill capacitors, but I'll guess excessive voltage here. Do you have something that might cause surges or waveform distortion?  \

The electric company put a monitor on the system for a couple of days, they then changed the transformer to a larger unit. The house has a 300 amp service and the other heat pump has never blown a capacitor. They both come off the same source. The units have a electric monitor and have always shown 118.9-124.7 vac. I'm not sure if a spike would register.

Same voltage rating on both capacitors? You might add a surge suppressor. Other ways to kill them involve heat - it normally runs cool?

2804021 VAL-SQ SE 120-120/240S/FM available from Phoenix contact will eliminate house surges  I'm putting it in my place.

http://www.phoenixcontact.com/surge..._48335.htm

Not an HVAC expert but a past drip under pressure of surge protection systems and components.

phase deviations???? the power company can monitor that.. known as power factor conversion. Messes with large capacitors.... corrected with really large capacitors at service entrance... usually associated with large 400 hp motors

The system runs when the desuperheater is disconnected. This is an install with (2) 5 ton units. The one without a desuperheater never has had an issue with blowing capacitors, now that the desuperheater is off on the other unit, the unit is fine. Could the desuperheater allow good subcooling and cause slugging to the compressor occasionally? This would blow a cap, right?

Posted By earthheat on 20 Apr 2010 08:59 AM
The system runs when the desuperheater is disconnected. This is an install with (2) 5 ton units. The one without a desuperheater never has had an issue with blowing capacitors, now that the desuperheater is off on the other unit, the unit is fine. Could the desuperheater allow good subcooling and cause slugging to the compressor occasionally? This would blow a cap, right?

You are taking a leap of faith I wont join you on.
I've never seen a DSH cause "slugging" nor "slugging" kill a capacitor. I'd look for another explanation......how is your DSH piped btw?
My failure rate of capacitors seems to have risen geometrically right around the inception of NAFTA.
j

I concur with Joe.

DSH incorporates a very small pump and results in reduction of superheat and possibly a bit of condensation of refrigerant immediately downstream of the compressor discharge.

I can't think how DSH presence or use can be linked to slugging a compressor nor how slugging relates to capacitor failure.

The system runs when the desuperheater is disconnected. This is an install with (2) 5 ton units. The one without a desuperheater never has had an issue with blowing capacitors, now that the desuperheater is off on the other unit, the unit is fine. Could the desuperheater allow good subcooling and cause slugging to the compressor occasionally? This would blow a cap, right?

The DSH pump is wired to the compressor contactor. If the unit runs fine without DSH it might be wiring or pump problem.
Make sure nothing is getting wet from a DSH water leak. I have seen a DSH motor weeping water.
I concur that slugging is not likely your problem.