AC Freezing Up - Montana Owners Club

Harold & Teresa · 05-23-2005, 09:08 AM

This weekend we were using our trailer and the AC froze up on us twice. The first time the thermostat was set on 72 and when it froze up I thought maybe the thermostat wasn’t working correctly. I purchased and installed one of the Hunter digital thermostats from Wal-Mart. After installation the unit was set on 73 and it froze up again. Outside temperatures were only in the upper 80’s and the fan was running on high. I spoke with a mobile RV repair man and he told me they were having lots of problems with the new Dometic AC’s freezing up. Has anyone else had any problems with their Dometic Brisk Air 15,000? Any ideas on what may be causing this issue?

azstar · 05-23-2005, 10:03 AM

Hi Folks,

We have had ours freeze up once. It was high 80's but high Humidity as well. We ran ours on manual high fan. This way the fan runs all the time and the compressor is allowed to cycle with Temp. It did help.

Happy camping

Montana_2779 · 05-23-2005, 11:31 AM

We're on Steve & Nina's bandwagon. We were told a number of years ago by an RV A/C tech to always run the A/C on high. We've had very few problems in a variety of conditions over the last 5 years (two difrferent manufacturers). If this doesn't reduce your freeze-ups, the next step would probably be a trip to the dealer/repair shop to have the freon level checked. Also, verify that there is nothing blocking the circulating air up on the unit (inside or outside of the cover).

Charlie · 05-23-2005, 05:28 PM

I have to duplicate what Pete says about running the A/C on high to prevent freezing up. Last trailer I owned had a Dometic A/C and it would freeze up running on low fan speed. I had the Monty freeze up the first time out because the weather was cool enough for the unit to cycle and for some reason I had set the fan speed on low. The first day that it was warm enough to keep the A/C running hard enough to keep it from cycling it froze up. I should have known better and from now on fan speed won't be changed. As Pete said, if it keeps freezing up, might want get the freon checked.

mazeeff · 05-24-2005, 01:52 AM

I'm confused here. The Dometic AC units used in the 2005 Montanas have freeze guard built in. There is a circuit and probe that go from the control unit in the ceiling to the evaporater. If the evaporator drops below freezing, the unit turns the compressor off and puts the fan on high. After the unit thaws, it turns the compressor back on. It works great. I'm concerned that maybe your unit does not have this feature, due to your comment about replacing the thermostat with a hunter. The new units are not compatible with Hunter. I would have thought that your original thermostat was either the remote based system or the digital Duotherm Comfort Control System. I find it hard to beleive that it was a older analog system, which are compatible with the Hunter replacement.

Montana_2779 · 05-24-2005, 05:54 AM

Good point, Mike! We have an old slide-lever analog tstat in our Mountaineer. We've had no issues under our current mode of operation, so the freeze guard never came to mind. For those with the freeze guard, that would probably be an item for the A/C tech to check during an inspection.

DHenry · 05-24-2005, 06:07 AM

Go to the Dometic site, they had a bulletin about the A/C freezing up. It has to do with the freeze gaurd placement and duct leakage if I remember correctly. We had the same problem you have described and I took it to our dealer, they adjusted the location of the freeze gaurd. I have not had it out in hot weather again to test it real well, but I guess I will see if it really did the job this next week at Lake Siskiyou at the get together.

Broome101 · 05-29-2005, 01:35 PM

This weekend ours froze up twice. this is the first time we have had to use A/C all weekend. temps outside were mid to high 80's. We have the CCC and freeze guard protection on ours but she still froze up. A/C could not keep the unit cool stayed about 79 degrees inside the coach. Will have to call the dealer on Tuesday. Hate problems but what can you do.

mazeeff · 05-30-2005, 12:24 PM

There are a couple of ways to prevent freeze up on the Dometic AC units.

1. Never use the "quick cool" function. This pumps the cold air right into the path of the return inlet. The colder the inlet temp the quicker the freeze up. Close the "quick cool" grate and pump the cold air to the locations a bit further from the inlet.

2. When it is hot and humid, don't try to run the AC down to target temp in one step. For example, if it is 90 outside and you want to get to 70 inside, follow this procedure.

a. Set temp to 85 and let cycle 2-3 times.
b. Set temp to 80 and let cycle 2-3 times.
c. Set temp to 75 and let cycle 2-3 times.
d. Set temp to 70 and let it run.

What this does is allows the system to remove the humidity from your trailer before hitting the target temp. The cycling allows the evaporator to thaw if it starts to freeze. High humidity is one of the factors in causing freeze ups.

3. Take the filter grate off, and verfify that the outlet and inlet sides of the AC units are completly isolated from eachother. In most causes you will find holes between the two, and this allows the cold air to return to the evaporator, where it quickly freezes. A little tuck tape should fix you up.

Broome101 · 06-04-2005, 04:34 PM

My dealer called me today to say only thing they could find wrong with our AC was that duct work had some leaks in it, they ran it appears to be fine. Do you think this could cause freeze up's? I do have the CCC with freeze Guard so I am little confused why it did not thaw itself out they said it was located correctly so who knows.
I am thinking of have the 2ND AC but in anyway since it is prepped for it, do you think it's worth the 2nd ac for assurance. For those of you that have 2 AC can you run them at them same time?

Montana_2753 · 06-06-2005, 09:42 AM

Here's my 2 cents:

Just got back from a week in Quartzsite, where it was VERY dry (read LOW HUMIDITY) with temps 95-106F. I have a second AC installed in the bedroom (a Coleman 15,000 unit because I'm going to be spending summers there as well). In the course of the week, the Dometic froze-up about 4 times and the Colman a couple of times. Went to an RV repair place to get input. It was suggested that I place moist/damp towels around inside of the trailer to up the humidity as this would help the AC run more efficiently and it would feel cooler. Didn't have the time to do it, but was thinking of getting a humidifier to do this. Both units had fans set on high with the Dometic's thermostat set to "auto" and around 74F-76F. I was told that some units are OK at around 76F, but if you go to 72F you could have freezing problems. The Coleman unit only has the manual knob temperature adjustment, so tried to keep it cycling in the 74F-76F range as well. I might add that I used the "quick cool" on the Dometic and that may have contributed to its freezing. Will try what mazeeff suggested, however I had the ceiling fan going so air was circulating fairly well so wouldn't think this would have been a concern. (Just a quick thought: What about putting some kind of a "shield" around the return [like the plastic vent air deflectors from Lowes or HD] to keep the cold air from going directly back into the return?) Thanks, DHenry, for info on Dometic site. Will be trundling over there as soon as I post this.

Thanks for everyones input!

Bruce

DHenry · 06-06-2005, 02:20 PM

We used our A/C at Lake Siskiyou a couple of weeks ago without any problems. We are taking the Big Guy to Las Vegas next monday so will really give the A/C a test.

cs413 · 06-06-2005, 02:31 PM

Ok - I guess I don't understand something. I had also always heard not to run your a/c unit on low speed. I had a 15K Duo-Therm on my Holiday Rambler for 10 years before I traded for the Monty with no freezing problems.....BUT, I never ran it on low either. So, I guess my question is....Why on earth would Dometic put a low speed setting on the fan if all they do is freeze up? They have to know that - they engineer them. It doesn't make any sense. I am having a second unit put on the bedroom tomorrow and I went with Dometic. I almost changed my mind and went with Coleman except I keep reading they do the same thing. So once again I ask WHY!? I guess that's a question for the manufacturers.

sreigle · 06-06-2005, 02:45 PM

I think that's a really good question. My understanding is the freezing at low speed is generally in high humidity situations but this thread seems to indicate low humidity is a problem, as well. We've had two fifthwheels with DuoTherms and both would freeze up in hot, humid conditions with fan on low. The prior two fifthwheels both had the Coleman and we only had one freezeup with those.

I think many folks have found freezeups related to the leaks in the return air area where it's sucking in the cold air. That's a separate issue from the DuoTherm low-fan freezeups. I think, anyhow.

We've been back in 90 degree weather with very high humidity (Kansas City area) for about 30 hours now and the AC has run a lot without a problem. But it's on high fan, too. It ran six hours non-stop with ceiling fan and two floor fans running to get us cooled down when we first arrived.

Montana_2753 · 06-06-2005, 07:58 PM

Steve:

If it appears, as mazeeff stated: '1. Never use the "quick cool" function. This pumps the cold air right into the path of the return inlet. The colder the inlet temp the quicker the freeze up. Close the "quick cool" grate and pump the cold air to the locations a bit further from the inlet', is correct, do you think my thought of:'(What about putting some kind of a "shield" around the return [like the plastic vent air deflectors from Lowes or HD] to keep the cold air from going directly back into the return?)' makes sense? Seems like this might form a barrier between the return and the "quick cool" vent so the cold air wouldn't be able to go directly back into the unit. I was using the "quick cool" setting to keep cold air in the livingroom/kitchen area because I had the second AC in the bedroom and didn't need the cold air from the back AC going there. Also, do you think the idea of using a humidifier makes sense?

Bruce

mazeeff · 06-07-2005, 01:57 AM

High humidity creates the freezing problem. The lower the humidity the less chance of freezing. You must have moisture to create ice! I think you will find that most freeze ups occur in hot/humid weather where the owner tries to go from 90 to 70 in one step. You need to stage it, as I described previously. Also, separating the inlet from the outlet will also help. Either by not using the "quickcool" or by adding a divertor. With a little trial and error, I think you'll find that you can prevent all freeze ups. In my old TT, we would freeze up within 10 minutes every summer in Texas. By using these techniques, we eliminated all freeze up conditions. We currently have a 2005 Montana which has the new "Freeze guarded" Dometic A/C unit. It does a good job of detecting the freeze, and cycles the unit to thaw it out. Works great!

DL N K · 06-07-2005, 03:05 AM

Our's froze up twice on the last outing also. Once during the day and once overnight, fan on "auto" both times. If I understand correctly, the freeze guard should should shut the compressor off and switch to high fan when it senses a temperature apporaching freezing and keep it that way until the coil temp comes back above the freeze point. If that system is working correclty, it seems that it should never freeze up????
We have been converted to the CCC thermostat.

mazeeff · 06-07-2005, 03:49 AM

Quote:

quote:Originally posted by DL N K

Our's froze up twice on the last outing also. Once during the day and once overnight, fan on "auto" both times. If I understand correctly, the freeze guard should should shut the compressor off and switch to high fan when it senses a temperature apporaching freezing and keep it that way until the coil temp comes back above the freeze point. If that system is working correclty, it seems that it should never freeze up????
We have been converted to the CCC thermostat.

You are correct in regards to how the freeze guard works. I forced ours to freeze up by routing the cold outlet air back into the inlet. It froze in less than 3 minutes. Once it got to 32 degrees, the compressor turned off, and the fan switched to high. The evaporator thawed very quickly, with a gush of water off the back of the trailer. Once the probe reads a higher temp, the compressor turns back on. Works great! If your freeze guard is not working, I would pull off the filter grate and look up into the coils, and make sure that the freeze guard probe did not fall out of the coils. I had to tie wrap mine to keep it in. It is just pushed into the coils, and mine was pretty loose.

sreigle · 06-07-2005, 05:16 AM

This is a good discussion. I appreciate the information. I think maybe we got lucky the other day when the AC, along with the ceiling fan and two floor fans, ran for 6 hours getting us initially cooled down. The Quick Cool was open for the first 30 minutes and we didn't freeze. I then closed it because the rest of the house was getting no cool air. I don't know the humidity percentage at that time but the temperature was about 93F. Early this morning the weather people said it was 75 degrees and 79% humidity so the AC started running early on. We also have no shade in this site until evening so have direct sunlight. Fortunately the AC does a good job of keeping it nice inside even though in the low 90's and humid outside. It does work a lot, though.

Montana_2753 · 06-07-2005, 12:38 PM

mazeeff: Thanks for the info. I have copied your suggestions and will try them the next time I'm in Q'site.

If I understand what is being said about humidity, then adding moisture to the INSIDE of the trailer would possibly contribute to freezing up, contrary to what the person at the RV repair place said? Or does the humidity just relate to the OUTSIDE humidity?

DHenry: Went to the Dometic site and couldn't find info there, but probably wouldn't pertain to me because I donot have the Freeze Guard.

Great information on what seems to be a very common problem. Went to RV.net and found similar discussion, so WE ARE NOT ALONE!!

Bruce

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