Tru Air icing up in heat mode - Page 2

DancinCampers · 02-10-2011, 09:33 AM

My Manual says there is a freeze thermister located on the outside coil, it opens at 18 deg +/- 3 deg, and closes at 38 deg +/- 3 deg, actual coil temp.

Thudman · 02-10-2011, 12:07 PM

My basement unit freezes up frequently (as in just now). 45* temp, 76% humidity (in Fla). Unit is new (5 mos old) & is a R-410A unit. Appears to be # 1 compressor according to DancinCampers (thx Dan). Spoke w/RVP but all they said was take it to a svc ctr. I'm in LP Heat now, waiting for the thaw out. Did not seem to have this glitch w/the old R-22 system. Ah, progress.

Thudman

DancinCampers · 02-10-2011, 12:40 PM

Thudman, is the unit (compressors shutting down when this frost occurs) or does it continue to run?

I don't know what the difference is in the R-410A freon pressure/temperature relationship vs R-22. If the unit is shutting down with that little amount of frost it may be that they have changed the value of the thermister that opens.

The outdoor coil of Air to Air heat pump systems will frost. The temp/humidity of the outside air will determine to what extent. I would think that at 45 deg, the frost on your coil should melt during the off cycles. But if it isn't, then it will grow during each cycle. Eventually it will reach the point where it blocks air from moving thru the coil. Then the freon will get colder and colder, finally reaching the temperature which opens the thermister.

Thudman · 02-10-2011, 01:33 PM

Dan, the unit shuts down; i.e. Set temp 72*, rm temp reaches 71* & unit comes On to heat; goes Off when temp reaches 73*. Does this for 2 or 3 cycles, then refuses to heat (shuts down) when room temp reaches 71* & lower. At 5* spread, LP Heat kicks in. It's in Elec Heat now & running. But will frost up soon & begin the cycle again.

Have no clue about Thermistor setting; but a few days ago RVP Tech said new T-stats have a different algorithm, with a 20 min delay (see earlier posts, this thread). But I did not change out my T-stat, so have the old algorithm. RVP said the old T-stat works OK w/new unit.

Just went out to look at outside frost & it's there! Me thinks RVP needs to adjust something, 'cause the unit is way too sensitive to icing up.

I've called three times to talk w/elec engineer (David) but does not call back.

Thudman

zippo · 02-10-2011, 04:40 PM

Quote:

Originally Posted by Thudman

Dan, the unit shuts down; i.e. Set temp 72*, rm temp reaches 71* & unit comes On to heat; goes Off when temp reaches 73*. Does this for 2 or 3 cycles, then refuses to heat (shuts down) when room temp reaches 71* & lower. At 5* spread, LP Heat kicks in. It's in Elec Heat now & running. But will frost up soon & begin the cycle again.

Thudman

The operation of your heat pump sounds very much like mine in my 2008. I have never seen ice on mine, but it seems to be very sensitive. I figure it is icing up as if I leave the heat pump off for awhile I have a large amount of water on the ground as it melts. It sounds like your LP comes on, just wondered if you are set to 72 and it shuts down at what temperature does the LP come on?? My LP never does come on. Over the winter I have found if I run a small electric heater along with the heat pump it seems to work much better. I think that is because the heat pump is not required to run as long. Shorter run time must mean less icing and it has time to melt off before it comes on again. When I called and talked to Coleman they said they think my thermostat may need to be replaced. My problem is it's still under warranty and in this area I can't find anyone that can work on it.

Thudman · 02-10-2011, 05:06 PM

I haven't allowed let the room temp to drift down in a few weeks, but when I did, the LP came On at 5* below Set temp. The unit is in Elec mode right now, with 43* & 73% humidity. There's moisture on the lower third of the condenser grill, so I expect it will ice up shortly.

And I'm on my fourth Tstat (as previously stated, current one is the old model). Guess I'll have to live with the situation since I'm out of OEM warranty & have $500 ded on extended insurance (aka Good Sam CSP).

Thudman

DancinCampers · 02-11-2011, 09:34 AM

Thudman, my guess would be your thermister is very sensitive, or value is at hi end of calibration.

One thing to remember, once tstat calls for electric heat, all further functions are controlled by pc board in basement unit, until tstat turns electric heat off.

During operation in heating mode, tstat only monitors room temp, comparing to set temp. Old tstat compares using degrees, new tstat compares using time (I Think).

Old tstat will turn off basement unit & turn on LP when it not only can't reach the set temp, but when room temp drops below it's 5 deg? spread. This can occur 3 times and then the unit turns off for 2 hours and runs on gas only.

After 2 hrs the basement unit will be turned back on, and 3 strike cycle will repeat.

I think the new tstat's will initiate your first strike when the heat pump is unable to reach set temp within 20 minutes, even if it is maintaining the room temp within the 5 deg limit.

Now throw into the mix the freeze thermister. This is wired in series with the tstat. It operates similar to the one on the indoor coil, which will turn off the unit in air conditioning mode when the coil freezes over.

Now, an additional wrench to muddy up the waters, in looking thru Rvomfort's tstat model manual online, it appears that the freeze circuit wires going to and from the pc board to tstat are not used on some models, in their place are Auto Gen Start wires.

If it was me, I would replace the outdoor coil freeze thermister and see if the operation was better.

Thudman · 02-12-2011, 06:39 AM

Last nite I had it on Elec Heat; got down to 33*. This morning it's 36*, 57% humidity (lower). The Elec Heat cycled On & Off (set temp 70*) all nite & this morning without going to LP. Humidity seems to be big factor in icing for that thermistor. I'll call RVP this week & see if they'll spring for change of my thermistor. BTW Dan, where is it located on the outside PC board & can I change it? I can rent a chain saw.

Thudman

pdq_bc · 02-13-2011, 06:26 AM

We were just in southern Oregon and had the same thing happen as Greg & Lynn

The heat stopped working in the wee hours of the morning (woke up cold).
And now, the heat pump does not want to "engage"; the sytem goes through a series of clicking noises (like it is trying to engage) but no heat comes out.

Furnace does work fine :-)

Any ideas on why the heat pump won't work?
and, any suggestions on getting it working?

thanks everyone!
regards, peter

FDchief · 02-13-2011, 01:15 PM

Peter, not sure what the clicking sound would be but hopefully someone will chime in and help you out. At least you still have your furnace.

pdq_bc · 02-13-2011, 01:57 PM

Greg..."the clicking sound" was as if the unit was trying to engage / turn on...
bets me!
pdq

DancinCampers · 02-14-2011, 12:10 PM

Thudman, I'm not not where they physically mount the thermister, my guess is on the suction line leaving the outdoor coil. More than likely need to remove the unit to replace. The wires should connect on the upper left corner on the PC board.

Peter, if the clicking sounds a coming from the tstat I would turn it off and then back on to see if that resets it. Also, sometimes the tstat switch needs to be wiggled after you move it to get good contact (I always set tstat temp below room temp before I wiggle the switch, to keep the compressor from cycling. Then I raise the tstat to see if unit starts.)

If the clicking is coming from the basement unit, I would suspect the #1 compressor start capacitor/relay. This results in very high amp draw on the one place panel if you are on 30 amp power or generator.