5 button Dometic thermostat not working

[harleyman134]

My 5 button Dometic thermostat is not working (no display) and I can not use it to run the a/c's. I tired to troubleshoot it by unhooking it and hooking up a phone jack to it and measure for 12 volts at the Black and Red wires, this did not show any power coming to the thermostat via the red/black wires. I found a troubleshooting manual for the thermostat and from my understanding the power is supplied from the control board on a/c to thermostat via this phone wire, it is also my understanding that a fuse should be in line betweeen the a/c and thermostat. I looked for an inline fuse on the front a/c and couldn't find one. If my understanding about a fuse is correct does anyone have any idea where the fuse might be located.

Particulars on my unit
2005 MADP 4304 with two 15,000 btu Penguin heat pumps.

If my control board turns out to be bad on my a/c is this a replaceable item? Also, is there any way to test the control board.

[Route 66]

The 12v is supplied from the Zone 1 AC control board which is usually the front AC.

I don't believe there is an inline fuse.

On my Dutch Star the 12v fuse that powered the front AC control board was in the toilet room cabinet next to the 120v circuit breakers and it was labeled "AC".

The rear AC control board gets it's 12v from the front control board also.

The control board is replaceable but I don't think there is much we can test other than 12v in and 12v out.

[harleyman134]

Dirk,

Thanks for the info, I dug thru my stack of owners manuals until I found the one for the a/c. Looking at the wiring schematic I found the three amp fuse I was looking for, it's actually located on the control board. Back up to the roof tomorrow to check out this fuse, if it's good I'm gonna check out the 12v in (found this on the schematic also) and if I have power here I guess my next action will to replace the control board. Does this sound about right.

[Route 66]

Did you find a 12v fuse in a cabinet that feeds the control board?

[harleyman134]

I had already located it, it was on a strip next to the circuit breakers in the bathroom cabinet and labled air conditioner. It was 7.5 amp and looked good, I checked it with my meter too.

[Route 66]

Sounds good.

However the control board may be pricey so changing parts without being sure of the fault can be expensive.

["007"]

Are you using this Trouble Shooting Guide in Quick Tips?

[harleyman134]

007, I'm using this information, that's where I came up with the "phone" jack idea. Thanks

[Romeo]

HarleyMan,

If you find out it is the thermostat (which is common) I can tell you where to have it rebuilt for $85, exchange. The guy that does it will send you one and you return yours. I tried to find my post re: this, in this forum, but couldn't find it. The "search" function isnt working for me. If you need the info I will look harder.

[RobRV]

The 3 Amp fuse is located on the Circuit Board(s) that are under the A/C Shroud (s). There is a small cover which You will need to remove in order to access the Board.

Some other things that You need to look carefully at are those 2 Telcom Jacks.

I discovered that one of them was badly corroded. So bad in fact that it could not be salvaged. I was able to source a direct replacement for the Jack and had a friend with a pencil type Soldering iron remove the Old Jack and install the New one.

I reassembled the unit and was delighted to find that everything is now working normally!

If You look closely at those Jacks they are very fragile. The Part number is
HWS5567 by Molex. You will have to order through a reseller such s Allied Electronics etc.

["007"]

Romeo here is your post on reconditioned thermostat.
Just had to look through 6 or 7 pages of your posts.

[Romeo]

007,

Thanks, I don't know why I was having so much trouble finding it.