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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8769
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a heat pump and ever since I got it I have been having

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I have a heat pump and ever since I got it I have been having a problem when it is very hot humid weather. It works fine during the day but every evening around 8:00 PM the pipe that goes into the heat pump frosts up and the pump keeps working but cannot cool the house. I have it set to 22 degrees. What is causing this??

Welcome to Just Answer!.

There are several factors...

Air conditioners are not designed to operate when it is cooler than 22C outside.... they tend to run the cold coil too cold in those cases, and freeze the coil... ice builds up on the coil blocking the air flow.

This a common problem seen when a house is warm inside and it is cooler than 22 or 23C outside... the coil begins to ice, then air flow is blocked, the room then does not cool... so the compressor keeps running and ices the coil.

If it is warmer than 72F outside and the unit ices, the cause is a dirty air filter, or restricted air ducting if you have a ducted system, or the unit is very slightly low on refrigerant.

If you give me the brand and model number of the heat pump... and tell me if it has duct work connected to it or not I can be a bit more specific with advice.

I will hold the question open on this issue with no time limit as long as you keep rating my remarks *positively.



Phil and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.

The heat pump is a Bryant. I don't know the model no.. It is connected to duct work. This is happening when the air temperature is above 22 degrees.

Hello again.!

Thanks for the data. If the unit is less than 2 years old, it was likely charged just a few ounces low on refrigerant.... or the duct work is undersized (thats common)..

We can determine which by using a thermometer to take the temperature of the the cold air register that is closest to the air handler.... and the *farthest cold air supply grill to the air handler..... and.... the air temperature at the return air grill **using the same thermometer**

Let me know what readings you get.

If the unit is older than 5 years or if you have pets, the cooling coil could be starting to clog up with dirt.

We can go from there.

Customer: replied 4 years ago.

The unit is about 6 years old. Should I get someone to come and look at it?

Hello again.

Qualtiy of service can be a little spotty at times... if you know of a good company in your area with a good reputation it would not be a bad idea however.

If you can do the temperature measurements I mentioned earlier, that would be a better idea...then when you call the service company you will have a better idea if its refrigerant charge problem, or a problem with duct sizing.

Let me know, we can go from there.

Customer: replied 4 years ago.

I will have to get a thermometer in order to do this procedure. I don't own one. Also, how do I know where the return air grill is? Margie

Hello again Margie,

A cheap thermometer from a dollar store, or a hardware store will work..

The return air grill is where the air sucks back to the unit in the house with the fan in it..
return air grills are larger than supply air grills, about 20 x 20 inches, more or less and can be in a hallway ceiling, hallway wall, or floor.... or next to the unit that blows the air around the house.

Let me know if that makes any sense.

We can go from there.


Customer: replied 4 years ago.

Thanks Phil, I have no idea where this return air grill is. There is a grill in my hallway but I'm sure it doesn't have a fan in it. Margie

The fan is not in the return air is a long ways away in the air handler that is in a closet, the attic or under the house as a rule.

With the unit running, the return air grill will suck a tissue up and hold it...if it does, it is the return air grill

Stay in touch

Customer: replied 4 years ago.

Oh!! then that register is probably the return air register. When I get the thermometer I'll let you know what I find out. I do notice that the air coming from the register in my bedroom which is the furthest away from the furnace, does not feel as cold and does not blow out as strong as in the livingroom which would be closest to the furnace. Margie

Hello again Marge,

thats good imformation Marge, and points to a problem with the ductwork being about 20% too small.

We can discuss solutions after you get me the temperature test results.