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Heat pump not working properly after hurricane power outage

4K views 26 replies 4 participants last post by  phuz 
#1 · (Edited)
First post here on DIY, but after recently purchasing a home built in 1988, I am sure I will be on here more often.
The home came with a nice 16kW Generac generator and on Monday night before the power went out, we were experiencing some brownouts. The voltage was dipping pretty hard. It went out shortly after and the generator kicked in, but it does not power the heating system, so I don't think that affected it. When the power came back on today, I noticed that the Aux heat was running, which I expected because of the drastic temperature dip, but it has continued to cycle on/off to maintain temperature. I also have installed a TED5000 energy meter a few weeks ago, and I know when the heat pump used to operate before, the total house kW usage was around 8kW. Today I am seeing it operate around only 3.6kW and then after it fails to heat the home, it jumps to 17kW when the strip heaters kick in.
The inside circulation blower is functioning and the outside condenser fan is running, but am I safe to assume that the compressor is not running and I should check the contactor?
Thanks in advance.
 
#8 ·
Well, I was wrong...it is NOT the compressor.
I pulled the panel off and both compressor and condenser fan are running.
After a few minutes, there is frost on the larger line coming from the compressor and it is obviously very cold.
The smaller line is hot and can be touched for a few seconds before needing to pull away.

A friends father works in HVAC so he gave a few things to try.
I turned on the A/C for a few minutes, then turned it off for 15 minutes, then turned the heat back on, in case the reversing valve was stuck or not properly seated.
When the A/C was on, the air coming out of the vents was cool, but definitely not cold. When I turned the heat back on, the air was luke warm again with just the heat pump running.
I measured a duct temperature on the first floor to be 81F. After a bit, the electric strips kicked in again, and within a minute the duct temperature was at 108F and slowly increasing.

He thinks something with either the expansion valve, reversing valve, or low refrigerant.
The unit is a Carrier 38YZA and refrigerant is R410A.

Not sure where to go from here.
 
#10 ·
How cold was the room when you got that 81 deg. air? Heat pumps never put out a great amount of heat but they put out less when they are low on refrigerant. Only guages will tell you if that is the case. Your energy calculations are a bit confusing. A heat pump will use the same energy whether it's low on charge or not. Only when the resistance heat kicks in will it go up. It's time to pick up the phone and decide who is getting the check........:laughing:
 
#11 ·
The room that was getting the 81F air was around 70F. I am not sure why the system would have lost refrigerant all of the sudden, but I am not convinced that is the problem. The energy monitor would show around 8kW anytime the heat pump was running prior to losing power on Monday. Now when the heat pump runs, it shows around 4kW and the house does not heat, so after a bit the electric strips kick in and it will jump to around 18-19kW. I know that a low refrigerant won't affect the current draw like that, but if one of the valves is failing to operate, would that prevent a load being put on the system, hence the reason I am only seeing half of the power consumption?
 
#16 · (Edited)
Well, a friend's father who works in HVAC stopped out last night and we looked at the system together. He put his gauges on the high side / low side and even though we didn't have the pressure standard, he said the pressures he saw didn't look like anything to be concerned about. After running for 10 minutes, the closest duct temperature was about 85 degrees. Using my energy meter, I can see that the heat strips are running almost every time the heat pump cycles on, and it isn't even waiting for a long delay. I also saw them running consistently on a 50 degree day, which I know is not good. Last night, we unplugged the heat strips and let the system run by itself. My power usage shows that the system came on at 1am and has been running since with the thermostat set at 70 degrees. Granted, it was a colder night last night, but it shouldn't have had to run nonstop to maintain that.

The outside unit is a Carrier 38YZA036 (3-ton) and the Air Handler is a FV4B. The paperwork I have shows it to be a 14 SEER system.

I've attached a picture to show the power usage (collected from my TED5000 unit). All the spikes above 15kW are the heat strips kicking in. Around 1am, you see the heat pump come on and not stop. In fact it is still running as I write this. I went out and looked at the outside coil and there is a very, very thin layer of frost on the coils in a horizontal pattern.
 
#17 ·
One thing that hasn't been mentioned (or I didn't see it) is that heat pumps will freeze up in cold weather and for that reason the reversing valve changes the direction of the refrigerant to thaw the outdoor coils. Unfortunately when this happens you are running AC in the middle of the heating season. It's also necessary. However when the defrost cycle kicks in it stops the outdoor fan and turns on the strip heat to overcome the cooling cycle. I imagine you could override the heat strips so they didnt come on when the unit defrosts but then you would be pumping cold air into a space you are trying to heat. Seems a bit counter productive to me. Your graph shows just how efficient a heat pump is.
 
#19 ·
So on a 40-50 degree day, it is normal for the strips to come on that frequently? From what I have read, the newer heat pumps, especially a 14 SEER unit, should be able to run without heat strips down to 30F or possibly lower.

No. It's an adjustment that can be made to prevent it from happening. It's a tricky thing though, it must be there when needed. Often it's set a bit higher....but it's definately not needed at 50 deg. And depending on the thermostat controlling it it may be difficult to dial it in.
 
#20 ·
Last night your area dropped to 25 according to wunderground. So it should have had to run for hours on end to maintain temp. What thermostat do you have?
 
#22 ·
Thermostat calls for aux heat.

Can't tell the model number of the stat by a pic. Some of them have the ability to do a time up to bring on the aux heat. Doesn't matter what the outdoor temp is.
 
#24 ·
That one doesn't have the time up feature. At least not in the install manual online.

I think I'd get a different thermostat anyway.
 
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