With the cold weather coming in, especially the cold and damp/wet we've got going on right now (temp is low 30s, just above freezing), the condenser unit for my HVAC (I think that's the term - the box that sits outside next to the house) is starting to get covered in frost. When we got the snow last month, it got completely coated.

Is this a problem? How do I prevent/reduce this?

Heat pump? If so its likely the ambient air temperature sensor or the defrost board. Basic operation is in heating mode the reversing valve makes the inside coil become the condenser and the outside one the evaporator. So the outside coil gets cold instead of the inside one. But in low temperature it has to stop occasionally and make the outside coil the warm one enough to melt any accumulated ice. This is controlled by the defrost board in conjunction with the temp sensor. I have one of my heat pumps doing this current and tech off to fetch temp sensor since the board swap two weeks ago did not fix the issue.
Also low system charge can cause this but normally you notice the evaporator freezing up on hot days.

saw your post about your condenser freezing up. You might call my son, Jim Wolf. class of 88 who owns Enviromax services. I started the company 42 years ago and Jim has it now and they do all types of a/c and heating. He seems to have a soft spot for fellow aggies because he sure gets a lot of calls from TXAGS. you can call him at 713-466-7555 or pm him at 88agswin. Hope you get it fixed before the weather gets worse. Thanks. Bald Eagle (Jerry Wolf)

Do you have gas heat? If so, the outside unit (condenser) won't be running when you have the heat on. It'll only be for cooling.

It's electric, and it's a heat pump. Got someone coming tomorrow to look at it.

(Sorry, Bald Eagle, I called them before I saw your post.)

Fortuitously, dinner tonight involves an oven baking time of 90 minutes, which makes the kitchen nice and warm without running the heater. Might throw some cookies in later.

We have a heat pump & our AC man says in this weather switch to emergency heat because they are pretty ineffective in extremely cold, wet weather.

no problem.. give us a call if you need any help

Definitely not. Heat pumps have auxiliary heat strips that act as a "back up" heat that will be activated at some point. I can definitely feel the temp difference when our aux strips kick in. All I've ever heard was emergency heat is a big no go.

Pretty standard for heat pumps. I've had them for the last 15 years. They will freeze up in 40 degree weather if conditions are damp. With weather like this, my units will defrost multiple times in a 24 hours period. My heat pumps have output reasonable heat down to the teens. You have auxiliary heat that may kick in if the heat pump can't get it done. When defrosting, your system runs ins air condition mode a f your heat strips will kick in the keep the air coming out of your vents from being butt ass cold...maybe even tepid warm if you have enough wattage.

There is ZERO reason to run emergency heat if you have a properly set up heat pump. In the 20s and low 30s your heat pump may kick in the aux strips if it's set up that way and you've asked more than it can handle with heat pump alone...like when the wife says it's too cold and turns your stat from 70 to 76. It ain't gonna get there in quick fashion so it may ask for a boost.

Also, many heat pump units have HALF the heat strip capacity of an all electric system. This strips are meant to be use with the heat pump and not alone unless...well, it's an emergency and that's the only option you've got.

It's a heat pump. That's the way they are designed.

Do not worry about it.

The unit will have a defrost cycle, either based on time or a sensor. When it goes into defrost mode, you'll hear the swish of the reversing valve. Then, you will see steam rising from the outdoor unit as it defrosts. This will happen any time your run heat, it doesn't matter if it's in the 50s or below zero.

I have seen heat pumps running in the lab at temps of -45. They're still more efficient than straight electric heat, but you will still need the supplemental heat strips to maintain a comfort level.

Are the aux strips only supposed to turn on when in defrost mode? That's the only time I've ever seen mine kick on.

I've had mine kick in a few times when it was really cold (in the 20s). The hot dust smell is quite noticable.

HVAC guy came out yesterday. Defrost board, along with some of the ice sensors, are bad. System is running in emergency mode until the parts come in.

And since it's a 22 year old system, looks like a replacement will be in the picture in the next couple of years. Joy.

El_duderino said:

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Are the aux strips only supposed to turn on when in defrost mode? That's the only time I've ever seen mine kick on.

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It depends on how your system is set up. Sometimes they are on timers and reserve their use until a set time has passed and the set point has not been reached. Sometimes they are locked out completely unless specifically requested. There are many strategies that thermostat companies use and the dealer or user can change as they see fit. Mine only come on when the heat pump hasn't made significant progress in reaching the set point. In the 30s if it's windy is when I've see the aux heat kick in.

Here's what our guy recommends as the temp keeps dropping - he's been in business in this area a long time & is very highly thought of. It's 27 here & so far, our heat pump is not having trouble keeping the temp at 68. I have seen it go into defrost mode a couple of times.

"Folks: If you have a heat pump, it will get frost on it occasionally. This is normal. It will automatically defrost. But if we have weather like what's coming, it can neither heat nor defrost. So switch it to emergency or auxiliary heat setting till this blizzard passes. Ice or snow can fall on and freeze the unit and/or get the blade out of balance. It's only called emergency heat so you won't forget to switch back. By Tuesday, temps should be a little more reasonable."

I believe my emergency/aux heat only kicks in, with the following scenarios:

1). when I manually turn it on at the thermo

OR

2). when the set point is >= 3* from the ambient temp

I don't believe it knows it has been on for X amount of time an will kick in - that is not how it was explained to me.

So, right now it's 24 outside and 67 in the house and the heat pump is running constantly. If I bump it up to 70, aux heat will kick in to get it there.

I have noticed over the years when it gets 33* or lower outside, the heat pump has a hard time keeping the house as warm was we like it - 70* by my thermo. It was explained to me - at this point run emerg heat or suck it up and wear warmer clothes around the house until it warms back up or use a small space heater in your room.

I've replaced my defrost module on each of the two units I have one time since I have been here 10 years. It will ice/frost up and then defrost - it's the loud swoosh you hear when the unit reverses. If you have lots of fresh ice on the bottom and around the unit, it's working as it should. Heat pumps were made for this part of the country when we get like this 2-3 weeks out of 52.

EDIT: the instructions on my thermo: https://2gig.com/wp-content/uploads/2015/12/CT100-Operation-Guide.pdf

DIFF (Used for multiple stage systems only, not on screen for single stage) The differential is the number of degrees between the room temperature and the Target Temperature at which the 2nd stage will be used. Default is 2F , range is 2F to 6F (1- 3C). Touch MENU and then DIFF. Use the arrows to set the DIFF. Recommend 2F for very cold climates and the 6F for warm climates.

So I have a 3* diff set right now...might change that to 1* for the short term

EMER (in HEAT PUMP type) If you set your CT100 for HEAT PUMP with auxiliary heat, EMER function is available on the MANUAL screen. If you touch EMER, it displays EMER|ON. Your HEAT PUMP is disabled and auxiliary heat is your sole source of heat. This manual override stays active until you toggle EMER off. Auxiliary heat is more expensive than the heat pump so use EMER only if the heat pump cannot keep up or is defective.