Any air conditioning/heat pump experts here? Help, please.

[flvegan]

I'm in Florida, and I'm on a typical central a/c and heat pump system. The other night, it got down to 29 or so degrees. I set my temp at 60. When I woke up, the outside a/c unit was frozen. Meaning the perimeter of the outside a/c thing had a coat of ice on it, but nothing on the interior. Tonight, it's not that cold, but it appears I might be in the same boat. There is no blockage, or so it seems.

Any ideas as to the problem? Appreciate any help.

[GOPisEvil]

1. Deleted.

Misunderstood the OP.

:blush:

[Name removed]

2. Deleted message

Message removed by moderator. Click here to review the message board rules.

[Lil Missy]

3. When mine froze up, it needed freeon. I don't have the heat pump part though.

The times my a/c has frozen up, even if it's 60' degrees, it's always been due to freeon. Once they fix that, I'm fine.

Hope that helps.

[petronius]

4. I think that's normal, but the unit should have an automatic switch to change

to AC mode when the ice builds up - it seems that that mechanism is not functioning properly. I don't see why it would harm the unit, but the efficiency of te heat exchange probably goes down when it's ice over...

[krispos42]

6. Ah, so they're suppose to do what I posted below automatically.

That makes sense.


Nice to see those college thermodynamics classes weren't wasted!

[madinmaryland]

7. Uhmm. A little sympathy for the guy in Florida!

Blanket knitting is a course he should have taken!

:nopity:

[petronius]

8. Yep, you've pretty much independently theorized the heat pump

Your Physics 101 prof would be proud - :toast:

The only part you left out is that there is supposed to be a heating element to warm the inside air while the AC cycle is on. This is probably prsent on the OPs unit, but if it's not going to AC this part isn't doing anything...

[krispos42]

5. You might be SOL

To pump heat inside, the outside unit has to be colder than the ambient air. This way, the outside unit (an "evaporator" when you're running a home-heating cycle) "sucks" up heat from the (relatively) warmer outside air and pumps it inside.

So the outside evaporator might be at like 10 degrees F, or maybe even colder. And all that wonderful Florida humidity frosted the evaporator right up. I don't see any way to correct this basic tenet of physics.


You could run the A/C on inside your house, that is, reverse the process and run a home cooling cycle. That would pump heat from the inside to the outside unit (which in this process is now a condenser) and get the condenser HOTTER than outside ambient. That would melt the ice but it would mean blowing cold air inside the house for a few minutes.


Or you could light a shitload of candles and cuddle up with your dogs.

Sorry, dude. A $30 plug-in heater is really what you need right now.

[Fenris]

9. Hmmm...

I'm assuming we're talking about the condenser here. The condenser should not be running in temperatures below 60 degrees. It's very easy to freeze and blow out the condenser this way, but you probably know that. The condenser should not be running in cold temperatures. You really need to make sure that the condenser fan is not running. There is an interior blower that moves the air from the heat pump, so there is no reason that the exterior condenser needs to be running. This probably sounds really stupid, but:

1) Make sure your system is set to "heat" and not "cool."

2) Turn of the A/C unit - there should be a switch near the condenser unit. This should prevent the condenser from running.

[Robeson]

10. Heat pump units are pretty typical for your region....

...it's the most economical. If you're wanting to upgrade to a full blown ac/heating unit that would warm homes in New York, then you'd probably be throwing money down the drain. You are not going to be experiencing critical climatic situations on a constant basis, so I'd just stick with the heat pump. They are not always consistent, but they are pretty consistent for the areas they are in.

[struggle4progress]

11. I was told by my AC folk to monitor my outside line and to get somebody to add coolant if it started

showing ice

[Lil Missy]

14. Freon.

[struggle4progress]

17. Freon

[Lil Missy]

18. Okay. I stand corrected.

Butt hole.

:P

[struggle4progress]

20. Everybody needs to have at least one personal character trait

[MajorChode]

12. Lots of things can cause it to freeze up

The evaporator fan may be inop. The fan should be running anytime the compressor is on.

The coils may be dirty. They should be cleaned once per year. Just take the panels off and wash the evaporator coils down with a garden hose.

The system may not be charged correctly. For this and other problems, you'll need to have the system serviced.

It could just be that because it is so cold the system is running all the time and eventually freezes up. It may not do it once the temperature gets warmer and the system is able to run at a higher duty cycle.

[NJmaverick]

19. This is the best advice offered. Major C covered everything

[TommyO]

13. You said no blockage

does that mean you checked and change the air filter? A clogged filter can cause exactly what you described by seriously limiting airflow.

[LostinVA]

15. This used to happen at my house in VA -- I was told I was running it too high

Or low. You know what I mean. Let it melt and then set it so it's not running as much. It won't make a difference anyway: below freezing, heat pumps have major diminished returns anyway.

[Lil Missy]

16. Dood. Freon.

And how the does a deleted comment show up on a thread like this? :wtf:

[Redstone]

21. I think you ran up agains the Laws of Physics. Those systems can only raise or lower

the air temperature by a specific amount (call it 30 degrees for the hell of it).

That says that no matter how long you run the heat on a 29-degree day, it'll NEVER get warmer than 69 degrees in your house.

The freezing, though? I don't know. Damn, 29 degrees in Florida? I'm not about to make any fun of you here; that MUST have felt cold indeed.

Redstone

[MajorChode]

23. This is not necessarily so

While there should be a 40 degree (or so) differential between the input and output, as the system changes the ambient temperature inside you still have that differential so the house will continue to get warmer or cooler. A good example of this is your freezer which can easily change the temperature by 80 degrees or more compared to the outside.

The problem is an air source heat pump has to draw heat from the outside in order to work, so the colder it gets the less efficiently they run and when the temps get below freezing they are no longer cost effective. This is usually not a problem in many areas of Florida because it rarely gets below freezing.

[flvegan]

22. Thanks everyone.

It did a partial icing again last night, but it wasn't quite as cold. I had seen in a previous apartment when a freon leak was present that the entire apparatus would freeze up. This was odd in that it was just the exterior of the intake panels. The fan was turning (sounded labored, but turning) and there was no ice "in" the actual a/c unit.

It's not supposed to be as cold tonight, so I've got a technician coming out tomorrow (no weekend/emergency rate for me) to take a look at it. Thanks to EVERYONE that responded. It put my mind at ease in helping me to think this just might not be a $3k repair, while still having heat and I appreciate it.

[Ikonoklast]

24. The unit should have a defrost cycle that automatically turns on

sending heat through the unit when excessive frost builds up. There is a switch that controls this on the external unit that fails over time due to pitting or corrosion on the contact surfaces.

I just replaced mine, the switch was $80, and the service bill total was $130.

But, like other posters noted, the system need to be fully charged with no leaks, or it will just frost up again.

[Turbineguy]

25. Does the thermostat have

a "Heat" setting? Perhaps the system does not automatically switch over. Refrigeration works by setting the 2nd Law of Thermodynamics on its head by moving heat from a hot place to a cold place, but still follows the law by making the refrigerant cooler than the place it cools and hotter than where the heat is ultimately rejected.

If your thermostat was set to 60 and the system was in the cool mode you would have been cooling i:e rejecting heat to the outside that was 29F instead of say, 80F and in the process overcooled the compressor discharge, leading to a severe pressure drop. Hence the frost.

When in the heat mode you are in effect cooling the outside and rejecting the heat inside.

[rainbow4321]

26. Freon leak

Mine does that sometimes.
I think at the time the coils needed to be cleaned, also... they had gotten dirty cuz I had not changed my a/c filter soon enough.