Heat Pump: Outside Unit cover'd w/ frost

[duckie067]

On the outside of our unit, there is a layer of frost on the outside. It is about 1 inch thick. There is heat coming out of our air vents but when the outside blower shuts off, there is no defrosting--the frost still stays there. We were told to wait for at least 2 hours and then monitor it which we did. The frost continued to build on what looks like a wire filter that wraps 2/3 of the way around the unit.

The tech told us over the phone it cold be a stuck valve and once the outside temps reach above 40*, then it will go back to normal. It did do that today. He stated it could also be the delay frost control panel.

We had our unit serviced back in September and the tech who did it said all was geared to go. I assumed he checked out the heat pump and such. I think I may be wrong.

I did research and what I read it could be the delay timer or coils. There are 2 pipe like hoses that go from the outside of our home to the unit. One is covered in insulation and the other is in another metal type casing or sheathing.

Can any one explain what coils are? Are they visible? Where are they located? Etc? I have read where the coils could be dirty or the sensors could be dirty.

Sorry for the 20 questions but the tech said to replace a defroster panel could costs 300 - 400 dollars.

TIA

Traci

[hoar]

I have same symptom.
Defrost cycle is not working adaquatly.
Today it got up to 50 F and It is now heating properly.
I am trying to determine what went wrong.
Most likely posibility in my case is not enough defrost time.
My unit works by going into defrost when conditions indicate frost conditions. Its not clear to me which system is in use here.
The coil is a coil of copper pipe in the outside unit. In your case it's the thing with all the ice on it. Its inside the radiator fins. If the temperature of the coil is below iceing conditions, sometimes assumed to be 28F, then the unit will go into defrost mode either for a fixed time or until the temperature comes up to a certain temperature between 50 and 80 F
If the control doesn't check often enough, or does not run long enough to get rid of the frost, then frost will build up.
I think it can go past a point where it never will catch up regardless of the control. Often, if you get it ice free by applying outside heat, then it will work until the next exceptionaly bad time.

The defrost cycle is done by:
Reversing the plumbing to make heat on the outside and cold on the inside (like airconditioning)
Turn off the outside fan
Turn on the aux heat so the house won't get colder.

[albright]

heat pump

a heat pump wont work below 50 deg. after that your auxillary heat kicks on.

[suprheat]

a heat pump will work to -10F. I don't know what planet he is from. Different manufacturers use different methods to figure if the unit needs defrosting. Some just use a timer combined with a ambient air sensor. Most have a sensor on the refrigeration line to along with an ambient air sensor to calculate a point to determine a defrost cycle. Others use a pressure switch along to determine pressure drop across the coil. Some have a humidity sensor along with an ambient sensor. Manufactureres use some or all of these methods in different configurations to determine when a defrost cycle is neccessary. My guess for you fellows is that one or more of these components have failed. Open up your unit and look around and/or consult your manufacturers website.