A/C Fan not cycling to High Speed - Montana Owners Club

Gkerlin · 06-04-2012, 04:57 AM

Sitting here at Lake Powell.
Temp yesterday was 104. Inside the best I could do was 84.

It took forever to cool down the coach after the sun dropped.

Unit is brand new so still getting used to the new systems.

Anyway - fiddling with the thermostat today, Running in Cool Mode I have both zones fans set to high. When I change the bedroom to low - it drops to low, then when high it goes back to high speed.

The living room however does not change speed and i think it is stuck on low. I know in the past its run faster because it got hard to hear the TV when it was on high.

sure could use max cooling power in these temps.

Anybody have any suggestions on what do do? Would shutting both down - turning off the thermostat and restarting have any effect... like rebooting?

Turn off the DC master power disconnect and restarting....?

Turn off A/C power and restart??

Anyone had this problem? The solution would be most appreciated.

**DQDick** · 06-04-2012, 05:05 AM

If he doesn't come on soon, pm Ozz. He has an HVAC business in KC and is our HVAC expert.

Gkerlin · 06-04-2012, 05:10 AM

Thanks.. I was hoping that Ozz would pick this up but didn't think to PM him.

I'll let him wake up first :-)

Tomorrow we are going to get high (altitude that is) where the air is a bunch cooler. If I can't get the a/c to cool the house at least I can move the house.

Ozz · 06-04-2012, 05:38 AM

Huh? Did someone say something...

I would try the reboot, soft, and hard reboot. Reset and power off..
They come out with new systems, new thermostats, updated control boards.. a guy really can't keep up unless I got all the updates from Duo-therm or whoever makes the electronics.
I would suggest reading all the operating instructions, if you don't have them, go on line and get them. If that doesn't work, call Duo-therm, and/or the dealership where you bought it.
Good luck!

Gkerlin · 06-04-2012, 05:44 AM

Thanks Ozz. Mama is cooking dinner right now before it gets too hot. (My vote was to go out but she said no)
As soon as she is done I'm going to shut off the a/c units, go out and turn off power at the pedestal and restart.

I've read the manual but nothing in there is really helpful, plus the front (bedroom) unit is responding to my inputs... just not the back.

I'll let you know what I find.

Gkerlin · 06-04-2012, 06:36 AM

Well I've done a system initialization at the T-stat, and a hard reset (turned off the power breaker at the pedestal outside, and turned off the DC power disconnect on the coach.

Turned it all back on and still the same condition.

I've read some things on line that suggest a possible capacitor issue or high speed winding on the motor.

With the front unit on high speed (yesterday it was on Auto) and a fan blowing air from the bedroom to the Living room, I'll see what sort of cooling temp we can maintain today. Supposed to be up in the 100's again.

Ozz · 06-04-2012, 08:19 AM

I think the most probable cause is the controls/thermostat, but it looks like a professional may be the final solution.
Does your thermostat allow just the fan selector to be used independent of the cooling operation? (high-low fan) Have you tried that, if so?

Gkerlin · 06-04-2012, 10:04 AM

Yes my thermostat has 4 modes: Auto, cool, heat or fan mode.
Then when in those modes I can select hi, med, low, or auto fan.

I've tried Fan mode, and then tried to adjust fan speed when in that mode to no avail. I can hear a sort of click, when the relay or whatever, sends the instruction to the fan motor but nothing happens. the fan continues to run on low

When I do this with the 2nd zone - the bedroom - it works as it should.

I've called Dometic and they've suggested that I see an authorized service center.

since we are reasonably comfortable in 100+ heat - and are going to be leaving this tomorrow for a cooler altitude I'm going to hold off getting it checked out.

Our travels might bring us thru Denver in a couple of weeks and perhaps there or before in Moab I'll get it looked at.

Thanks for asking

Ozz · 06-04-2012, 10:42 AM

OK, the click is the relay I imagine, in that case it can either be the control board (relay is there) ...probable..or the motor... far less probable. The service guy is probably the best bet. Running on low, check the coil once and a while it could freeze up. There is a freeze control, but it could be located wrong, or it may not work. Best to check for freezing coil once and a while. Low speed lowers the evap temp and will freeze even when real hot out.
Good luck.
Ozz

Gkerlin · 06-04-2012, 11:12 AM

How would I prevent freeze up. Just shut it off if it started to look frosty?

The RH here is about 6%.. very dry. Still a concern?

Gkerlin · 06-04-2012, 11:19 AM

Never mind Ozz... it is froze up! Should I shut it down or just run the fan in fan only mode to defrost it?

looks to be frosted - not real iced up.

Ozz · 06-04-2012, 01:06 PM

I spoke with Greg, he is OK now.
Ozz

Gkerlin · 06-04-2012, 02:08 PM

Folks... an update as to what seems to have happened.

I had my fan speeds set to Auto. The mode was Cool. Both units (Front and Back) have been working overtime for days. I've had both direct vents shut so that both units feed the ductwork.

I'm not sure why - but my Living Room unit froze up.

so when I would cycle the fan from auto to high to medium and to Low - I could hear the relay or whatever click, and I would notice the slightest imperceptible change in fan speed but not the normal amount so I assumed that I was stuck on Low speed.

Thanks to Ozz who warned that being stuck on Low could cause Ice to form, I looked up inside and sure enough I was frosted over. Not big time, but enough to (I assume) cause a restriction in airflow that made it seem like the fan was not cycling speeds.

I opened up the direct vent on this unit, left the filter off, and ran the fan only and in about 15 minutes I was clear of frost, the unit was putting out it's normal blast of air, and where yesterday at 104 the best I could get inside was 84 degrees, today at 102 I'm sitting here right now at a comfy 72.

So.. Why did the unit ice up in the first place?

That one escapes me at present. Was the two units pumping into the same ductwork causing too much back pressure and caused the LR unit to not have enough airflow over the coils?
Should one leave a little bit of the direct vent open when the two units are both pumping into the ducts?

I'm not sure but i'm going to keep a closer eye on the coils from now on to see if I can figure it out.

For now - Let me just say I'm COOL on the shore of Lake Powell.

Thanks for the input Ozz.

Wahweep Campground - Page, Az

**DQDick** · 06-04-2012, 03:55 PM

Check to make sure your intake filter is clean. We have cats and so ours needs to be rinsed out on a regular basis. If that's not the issue then it's running them both into the duct work. I usually dump most of the living room out into the room and run about 3/4 of the bedroom one into the vents, but that's just how we like it, others may reverse that.

scductman · 06-26-2012, 05:31 PM

Ozz is right it may be the freeze stat located in the wrong place or they will go bad. I had one in a sob that never worked rite from day one. I put up with it for two summers before I changed it and had no more problems. Make sure it is close to the bottom of the coil.
Bobby

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