Heat pump package unit hard start only when cold.

[jjacob]

Hello all,
I am a homeowner with a one year old Nordyne (NuTone) DF6SF Package unit. This is a 15 seer two stage heat pump with two stage gas emergency heat. 3 ton unit.

The unit performs excellent both in cooling and heating until the temperature gets down to around 38F. I have the thermostat set at 31F for switchover to the gas heat.
Above 38F the unit performs perfectly. Around 38F and below when there is a call for heat the unit turns on, there is a buzzing sound (compressor trying to start?) for around 5 seconds, the coil fan turns slowly about one revolution and then everything stops. About ten seconds later the unit trys to start again (same buzzing) but this time both the compressor and the coil fan start and run. Everything from this point on is normal. It never fails to start on the second try (although with the buzzing noise at start). The breaker (40amp) has never tripped.

My tech installed a factory hard start kit. This does not seem to have made an improvement. He thinks the compressor might be bad.
Both the regular start capacitor and the hard start capacitor both were tested with a capacitance meter and are fine. This check was done at an outdoor temperature of 50F.

The 40 amp breaker is new, the outside disconnect is new, and the wiring from the outside disconnect to the unit is 8 gauge and is new (a run of only 7 feet). Wiring from the breaker box to the outside disconnect is 6 gauge and is original wiring.

My questions are does this sound like a bad compressor? Is it possible that the start capacitor is bad at only low temperatures? Since the unit runs perfectly at temperatures above 40F I have my doubts about the compressor being bad.
Thanks in advance for your advice.
John

[Hwolfe]

Tell tour technician to check the crank case heater.

[jjacob]

Thanks for the reply. I am fairly certain that a crankcase heater is not standard on these units. Are you saying that one should be installed?
Thanks,
John

[Hwolfe]

Yes. And with it being a heat pump it should have some type of crank case heater or way to heat the oil in the system at low ambient temps.

[BaldLoonie]

Crankcase heaters with scrolls are rare on most brands. Nordyne uses them on splits but then they have much higher refrigerant capacities than packs and the evap could be above the outdoor unit. But certainly a cheap thing to try for the dealer. Beyond that, change the unit. If you are the original registered owner, they don't change compressors.

[jtrammel]

Crankcase heaters with scrolls are rare on most brands. Nordyne uses them on splits but then they have much higher refrigerant capacities than packs and the evap could be above the outdoor unit. But certainly a cheap thing to try for the dealer. Beyond that, change the unit. If you are the original registered owner, they don't change compressors.

I think 2 major components have to fail in 10 years to qualify for the "quality pledge" replacement of unit if thats what youre referring to. To the op I agree with others, try a crankcase heater.

[jjacob]

Thanks to all who replied. So the consensous is that I should have a crankcase heater installed? These are generic units? I noticed in the Nordyne literature for this unit they do not list an optional crankcase heater, only a "low ambient kit" which is something different. Is there a particular type or brand that I should have installed?
John

[Tommy knocker]

Yep

[BaldLoonie]

The dealer can order a heater for a FT4BD split unit. That should fit your compressor.

[jjacob]

Thanks BaldLoonie!
John

[jjacob]

Well, turns out the compressor has a crankcase heater on it from the factory. Heater is working. Trying to get a hold of my technician for him to come out and look at the unit. Something is definately wrong. I was outside by the unit when it was around 40F outside. Unit did the buzzing, no start, then the second attempt it started and I heard a loud "whooshing" sound of fluid moving quickly through a pipe.
I checked the Nutone website and I believe that if the compressor is bad they will replace the entire unit. This unit was put into service in December of 2010.
John

[SBKold]

Well IMO you guys are barking up the wrong tree. Why would the compressor not starting have anything to do with fan motor?

Sounds like you have control issue and contactor is closing momentarily then opens.

[jjacob]

SBKold
Why would it be temperature sensitive? It only does this when the temperature is below 40F.
John

[SBKold]

That I cant tell you exactly but if the compressor alone was culprit than the fan would run and you may not even notice the compressor starting momentary.

[jjacob]

So as a follow up, the unit now seems to be running fine. I finally got a tech out here who was very good. Has a good diagnostic head on his shoulders. He determined from my description that the issue was in the defrost function of the unit because the problems were only evident at temperatures below 40F, and the crankcase heater was working fine. He investigated and found the thermal sensor inside the package unit was loose and became dirty. He ordered a new sensor. When it came in he cleaned the pipe surface, installed the new sensor and correctly wrapped it. Now the unit works properly.