We don't seem to be too helpful with this.

Nobody seems to be. GRAR.

No relevant experience or I'd sure chime in.
Wait, since when has that stopped me?

Yeah, it's so specific. Blah.

Well, I have no specific experience, but I can offer this technique: Screechy noises in machinery can be isolated more effectively by using any solid object as a stethoscope. Often the tool of choice is a big honkin' screwdriver, but be mindful of picking something that won't electrically short anything out. Broomsticks work nicely too. Place the tip of the screwdriver against the thing you suspect is making the noise, and rest your ear on the handle end of the screwdriver. It will be noticeably louder when you're on the noisy thing. It's usually a bad bearing, or sometimes gross misalignment.

Also, keep in mind that one failed part can often cause overloaded conditions in other nearby parts, shortening their lifespan sigificantly. For example, a motor with a seized bearing might still turn, but will draw lots more current.. That extra current draw can fry the motor controller circuitry, and that will still be a problem when a replacement motor is fitted.

Also, keep in mind that one failed part can often cause overloaded conditions in other nearby parts, shortening their lifespan sigificantly.

That's a huge concern of mine. The problem I have is as much with the home warranty company as with the seemingly incompetent technicians they've sent out so far. They fixed the screechy sound, but it caused this condenser coil to ice over. The ice covering the coil blocks the airflow, at least partially, and so there's strain on the rest of the system. If they just had someone find and fix the right thing right away, then I wouldn't need to worry about the other parts failing.

We'll see. They have a third service company coming out tomorrow.

I don't know much about furnaces but, given that you say it is also your air-conditioner, I'm guessing that this is actually what we would call a reverse-cycle air-conditioning unit. Are you sure that the condenser icing up is such a problem? What symptoms are you seeing that this is causing 'significant strain to the unit'?

I'm not trying to be smart, but we sometimes look at things more closely when they have been playing up than at other times. Maybe the ice has been there all along and you haven't noticed? Another maybe is that the ice is normal, but wasn't there before because of the previous fault?

You're right that it's a reverse-cycle air-conditioning unit, a.k.a. a heat pump. Thanks for the search term.

So, from Wikipedia:

Heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 40-55°F (4-13°C), because heat pumps become inefficient in more extreme cold. This is due to the problem of the outdoor unit's coil forming ice, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil back to being the condensor coil so that it can heat up and de-ice.

It has been cold this winter, much colder than usual. The problem is that it's not heating up and de-icing as it should. The ice builds up over the condenser coils, blocking air flow. The evidence of strain is just common sense. If you're supposed to have air flow through the unit for it to work, but the place where the air goes is blocked, it will make the motor strain. Yanno?

That was really helpful, dg. I didn't understand that my heater IS an air conditioner that works backwards to do the heating part.

Four different HVAC technicians have looked at it so far, and they agree that there's a problem, since it's not functioning correctly, but their tests aren't showing the cause of the problem. The usual suspects test out as working as they should.

OK, I'm starting to feel at least like I understand how this works a little better.

Could it be that it's simply too cold for it to work properly? My guess would be that the '... temporarily switch back into the regular air conditioning mode ...' thing is done via a timer. If the temperature outside is cold enough that the timed switching back to heat the condenser isn't long enough to melt the ice because it's too cold, you will see the symptoms you have.

Is it possible to find out the recommended temperature range of the unit? If you are operating outside that, there may be nothing wrong with the unit except that you are trying to make it do something it can't.

I wouldn't be too worried about strain on the rest of the parts because of the condenser being blocked - the fan will still keep pushing air around regardless and it doesn't care too much if the way ahead is blocked (I think). It will, though, seriously reduce the unit's effectiveness in warming your house, resulting in lower temperatures inside, meaning the unit will run for longer trying to bring the temperature up, meaning more strain, more ice on the condenser and higher power bills.

Ice on the condenser means it needs some refrigerant added to the system 90% of the time. Yes, this sounds converse to think that adding refrigerant actually makes the system *not* ice up.

The system is not 'straining' or harming itself in a traditional sense of strain. Don't sweat that concern.

I think that when they fixed the screech (probably a motor, fan, or belt issue) they could have accidently let some refrigerant out while attaching the test gauges, or when they were finished they did not tighten down the test fittings. Or they could have left one a hair open to slowly slowly slowly bleed out refrigerant so they get a service call next year.

Although any AC drawing will show the necessary expansion valve (liquid refrigerant enters, valve essentially works akin to a fuel injector in a car and 'squirt' out it comes in a vapour) in the 'how it works' drawing, there are other valves that regulate the flow through the expansion valve. TXV (also called a TEV) valve
Probably a confusing link; picture a thermostat in a car regulating the flow of coolant (hey, thats what refrigerant is!)

If the refrigerant charge is correct; then a faulty valve (HVAC how it works drawings always show the expansion valve; they do not show the regulating valves of which there are seveal different types...TEV, TXV, capillary, TEEV, ...) would be the problem.

The defrost timer for the condensor could be set for too little time; or it might not be working at all.

1) Is refrigerant charge correct in unit?
2) Defrost timer set correctly? (this might have been accidently disconnected or incorrectly adjusted during the initial screeching repair)
3) Probably not a valve issue like linked above; but could be.

Stewriffic, What make and model is your unit?

This might be a little in your face to do, but it will ensure the techs are real techs.

If the techs don't have their EPA certs (Have to get type I (small systems) and II (large systems) to get type III (all systems and removal of refrigerant), then they are *not* supposed to be able to handle refrigerants or work on HVAC equipment.

The EPA cert is a small drivers license size laminated card. It will say Type I, II, or III. Again, no card means they are NOT supposed to be doing any work on an AC. There are no 'cardless training/apprentice programs. Supposed to always have EPA cert any time HVAC is being serviced.

Thanks, Buzzman! It's a Kenmore, PHAD30N1K6, and it also says PYMC30G6.

Ice on the condenser means it needs some refrigerant added to the system 90% of the time.

That was their first attempt at a fix.

The defrost timer for the condensor could be set for too little time; or it might not be working at all.

The guy I spoke to earlier today, who will be coming out tomorrow, suggested the defrost timer as a possibility. He also mentioned something about the board.

Here's hoping!

TXV valve for your model.

Defrost board for your model.

I really don't imagine a valve would go out so early in a products life cycle; the valves usually work forever (unless something foreign gets into the system dust, debris, wrong type of refrigerant added into system (there are dozens of different refrigerants; many don't mix well with others), incomatible type of oil (ditto for the mixing well with others).

Debris would possibly clog the system or stick a valve open or shut. Wrong oil breaks down the refrigerant and oil mix which would harm the compressor by not lubricating it correctly.

Probably an electrical thing = board or timer, hopefully it just did not get switched back on after the first repair (of the screeching).

Hope this helps, please let know when it is solved.

Guy who came out today said it was the defrost board and sensor. He's going to replace it by Wednesday. I'm so cynical as to doubt whether that fix will work, and yet not so cynical that I've lost hope. Maybe, just maybe this guy will fix it!

Yeah, hope for best. As I read it; you are still under warranty so that is a good thing.