View Full Version : Heat Pump Defrost
01-25-2010, 09:54 AM
I have an Amana Distinctions Heat Pump. It is only 2 years old at most. We moved into the house this past summer. I found that the unit goes into defrost mode very often. Our system has natural gas as the aux heat. The outside condenser is going into defrost almost every cycle. This happens more often when the temperature is about 45 degrees and below. I am seeing moisture on ground outside the heat pump, so there is some condensation/defrost. Inside the condensing unit, there looks to be a stat/dial that is set to 38. I assume this should shut the unit off at 38 degrees. It does not. The heat pump runs all winter, even at 20 degrees (goes into defrost cycle of course).
Is there any suggestions on how to check if the internal outside air sensor is failed? There does not seem to be a probe anywhere, so maybe they did not hook up a sensor.
Why would the unit be going into defrost at 45 degree outside temperatures?
I ma going to have to get someone out to look at the unit, but I like to try and understand the potential issues before someone comes out to look at the unit.
01-25-2010, 10:24 AM
Not a pro, but I believe the condenser will go into defrost after "x" minutes of total run time at a condenser coil temp of "y" degrees.
The run time is selectable from 30, 60, or 90 minutes. I believe the factory setting is 30 minutes. I changed mine to 90 minutes without any frosting issues.
01-25-2010, 10:34 AM
Do you know where the setting is to change? This should prevent the unit from going into defrost mode within 30 minutes. If the temperaturew is cold outside, the unit will go into defrost mode everytime it comes on.
Is the unit going into defrost mode oftem ad for the compressor? Use a lot more energy?
01-25-2010, 11:07 AM
There should be a control board next to the contractor that has jumper pins on it to change the defrost sequence/time .. Your system needs defrost to operate and protect the compressor. It is possible that the system is slightly under-charged causing a pre-mature defrost and should be checked in the cooling mode once the home is warmed during the day. It's also very important that the outdoor coil is very clean. Once it is clean and dry you can spray/coat it with a little WD40 and this will keep it in heating mode a bit longer cause it will reject the ice more.. Amana/Goodman did have a batch of bad defrost control boards in which operated on continous time that was redesigned later. :pop:
01-25-2010, 12:16 PM
Use a lot more energy?
Yes. Assuming your house is all-electric, the aux electric strips in the air handler energize to temper the cold air from the defrost cycle (condenser is in cooling mode during defrost).
You want to minimize unnecessary defrost cycles.
01-25-2010, 12:32 PM
The house is not all electric. It has natural gas as the stage 2 (aux)/emergency heat. When it goes into defrost, the furnace kicks on and counter acts the defrost mode and heats the house.
For now, I have the unit in EMHeat mode to lock out the compressor, until I can figure out why it goes into defrost so often and I can get pay someone to come out and fix it. The unit does not operate in heat pump mode due to the EMHeat mode.
01-25-2010, 12:36 PM
Post #4 gives good advice on having the charge checked in the summer. You want the charge checked / adjusted based on superheat and subcooling.
Have you set the defrost time to 90 minutes to see if your defrost issue has gotten any better?
01-25-2010, 02:00 PM
I am at the office, but I plan on checking the defrost timer this evening when I get home
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