AC problem

[sk734]

My auto fan hi low system keeps changing speeds on its own. Anyone changed control board and thermostat to fixx this? My current board is 3313199.000 and thermostat is 3313195.012. This is a terrible system made by Dometic. New updated system from Dometic is available but I am not sure it will help. Kit# 3316230.014. Thanks for your help in advance.

[Learjet]

from the manual for my thermostat:

"Special Features

Auto Fan

When auto fan is selected the fan speed will vary depending on the
difference between the temperature set-point and the room temperature.
In auto fan the compressor and fan cycle On and Off with the
thermostat.

When the difference is:
>5º The fan operates on HIGH
<4º The fan operates on LOW"

The fan will stop and restart when it changes speed and the compressor will continue to run. Thought it was broken like most when I first got my current rig.

[Learjet]

sk734 wrote:
Update
Dometic 3 wire single zone ac. Changed board and updated stat. Runs then stops until reinitialize or turn off and back on? No ice up works great when running. Could use some help. Anyone know the cure? Thanks in advance.

My bed room does that if I leave it on LO fan overnight....I just leave it on HI fan and its happy.

[rjsurfer]

sk734 wrote:
Update
Dometic 3 wire single zone ac. Changed board and updated stat. Runs then stops until reinitialize or turn off and back on? No ice up works great when running. Could use some help. Anyone know the cure? Thanks in advance.

I have the same problem with my single zone unit. AC will run until temp is reached then shut off but won't come back on. I have to run through all the thermostat settings then it will restart.

I don't think it's a nice up issue either but haven't gone on the roof and checked yet.

Ron W

[sk734]

Update
Dometic 3 wire single zone ac. Changed board and updated stat. Runs then stops until reinitialize or turn off and back on? No ice up works great when running. Could use some help. Anyone know the cure? Thanks in advance.

[Just_Wandering_]

Your AC is working as designed. It is designed to run on high fan until within a certain preset temp then reduce to low fan to hold the temp.

[sk734]

No I have not. I will talk to them-good idea. It's to bad this auto fan system driven by temp has come into play. I was perfectly happy with my prior rv that had a manual 2 speed fan setting. They are trying to build a better mouse trap?

[WTP-GC]

I don't know why you would change the board AND thermostat. It's not likely that both are bad. I don't actually think it's likely that either are bad. Speaking as someone who has aimlessly thrown money at many problems over the years, I'd be hesitant to change anything until further diagnosis is performed. Have you contacted Dometic yet?

[sk734]

Thanks for all the post.

[sk734]

I have also Taped off any leaks some time ago.

[sk734]

WTP-GC wrote:
If I understand correctly, when the AC fan speed is set to "Auto" it will change between high and low on its own. Is that right?

If so, then that's the basic design of the system. If you find it switching frequently (comtinious changing every 30 seconds to a minute), then it's highly possible you have a duct leak at the unit. My brand new Grand Design had this problem from day one. Over on the GD owner's forum, this problem and solution have been discussed at length. If you remove the shroud (really easy), you might find that the duct is not well sealed where it interacts with the return air duct. This causes the thermostat to get erroneous readings and short cycle. The solution is to get duct tape and seal up every single nook and cranny in there that would allow this to happen. It's pretty self-explanatory when you're looking at it. Put the shroud back on and you're good to go.

Of course..."IF" this is the problem you're experiencing...

Yes that is the case. I am wondering if I going to have to change out the board and stat.

[wiredgeorge]

Almost all ducted a/c systems are not sealed well at all. First, remove the cover over the inside a/c unit and note that there was a feeble attempt to seal between inlet side and exhaust side. Buy some A/C vent tape and fix the problem. Also note where the outlet duct enters the ductwork, this may also need some sealing. Pull off all overhead vents and note that the sealing with A/C tape is similarly poorly done. Some folks put a barrier (styrofoam is the material of choice) at the ends of the run if the duct just dumps in to the void beyond. Cleaning up the sealing issue greatly enhances the effectiveness of the A/C system.

[WTP-GC]

If I understand correctly, when the AC fan speed is set to "Auto" it will change between high and low on its own. Is that right?

If so, then that's the basic design of the system. If you find it switching frequently (comtinious changing every 30 seconds to a minute), then it's highly possible you have a duct leak at the unit. My brand new Grand Design had this problem from day one. Over on the GD owner's forum, this problem and solution have been discussed at length. If you remove the shroud (really easy), you might find that the duct is not well sealed where it interacts with the return air duct. This causes the thermostat to get erroneous readings and short cycle. The solution is to get duct tape and seal up every single nook and cranny in there that would allow this to happen. It's pretty self-explanatory when you're looking at it. Put the shroud back on and you're good to go.

Of course..."IF" this is the problem you're experiencing...

[wrgrs50s]

If it's a dometic unit and thermostat, it's a standard issue. Mine has done that since new and I was told it's designed to operate like that in auto mode. I got tired of it and run my fan in Hi, or low mode instead of auto. The other odd design flaw is that if you run your fan on high or low and then need to run your furnace the AC fan will will run when your set your furnace to on. The fix for that is to set your fan mode on auto when using the furnace.

[MFL]

You don't say what year model, but most newer Dometic are designed to change on their own when in auto mode. Mine works great, starts on high, when set temp is 6 or so degrees lower than actual temp, and stops, changes to low, when getting close to set temp.

If yours is continuously changing from high/low, when set temp/compared to actual does not warrant, then you have an issue. If this is the case, I'd just set on low or high, as needed. Automation is great when it works!

Jerry