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Topic: No Power to Thermostat (Read 497 times) previous topic - next topic

No Power to Thermostat

****UPATE****

Just checked it again.  Turn the switch to On, and it worked.  And just to let you know, we have had this motorhome for 4 years, and use the A/C often, both at RV Parks, while traveling down the road, and when parked at the house.  So, I'm going to assume that it is probably a faulty thermostat.  I guess I shouldn't be surprised since it is the original unit and is 27 years old. 

We have a 97 U295, with the Duo-Therm (Dometic) thermostat.  I just ran the A/C's yesterday, with no problem, but went to turn the A/C's on this morning, to do a little work inside, and nothing.  No power, lights, or anything.  I checked the breakers at the foot of the bed, reset breakers, unplugged and plugged back in the shore power, ran the generator, but get no power to thermostat.  I literally did nothing since yesterday except turned off the power to the thermostat. 

Any ideas on what to check?

Re: No Power to Thermostat

Reply #1 –
Did the salesman switch get accidently turned off at the door?

Re: No Power to Thermostat

Reply #2 –
Turn the switch on bottom of thermostat.  It is showing off.

Re: No Power to Thermostat

Reply #5 –
Take the cover off and remove it from the wall.  There's an RJ11 phone type jack that connects it to the AC and power.  It may be loose, not seating correctly, or need some cleaning.  I believe the other side of the cable connects to the front A/C unit, although I cant remember exactly where.  Someone here will. :)  Mine was a little loose and that solved the issue for me.

Re: No Power to Thermostat

Reply #6 –
Quote from: Brucep86 –
No, it's on, although I don't know that would affect the A/C thermostat.

It kills most of the 12V power to the house part of the coach, including the thermostat.  The thermostat itself is powered by house 12V.

Re: No Power to Thermostat

Reply #7 –
Quote from: craneman –
Did the salesman switch get accidently turned off at the door?

In this coach I do not believe that the salesman switch will kill the AC units. The front AC unit has a circuit board that has a connect from the thermostat, 12 power, and jumper to rear AC unit.  If I remember correctly to get to this circuit board is to get on roof, remove out cover and there is another cover under that will get you to the circuit board.

Wish I remember where the circuit breaker is for the AC units but it is either under the cover in front of passenger seat or in compartment on drivers side.  The breaker is labeled.  I once had to kill power to the circuit board to reboot it when it was not working right(don't remember what it was not doing as to why I disconnected 12V power to the AC board. )

Re: No Power to Thermostat

Reply #8 –
Quote from: turbojack –
In this coach I do not believe that the salesman switch will kill the AC units. The front AC unit has a circuit board that has a connect from the thermostat, 12 power, and jumper to rear AC unit.  If I remember correctly to get to this circuit board is to get on roof, remove out cover and there is another cover under that will get you to the circuit board.

Is that because the IH has Firefly integration?  Brucep86's coach is a 1997.

Re: No Power to Thermostat

Reply #9 –
Quote from: Brucep86 –
****UPATE****

Just checked it again.  Turn the switch to On, and it worked.  And just to let you know, we have had this motorhome for 4 years, and use the A/C often, both at RV Parks, while traveling down the road, and when parked at the house.  So, I'm going to assume that it is probably a faulty thermostat.  I guess I shouldn't be surprised since it is the original unit and is 27 years old. 

Forum member Jim Frerichs repairs the thermostats

Dometic 4 button thermostat repair

Re: No Power to Thermostat

Reply #10 –
Quote from: Michelle –
Is that because the IH has Firefly integration?  Brucep86's coach is a 1997.
,
No, 2014 IH45 has somewhat same system as the 1997 U295, no firefly in my coach on AC's.

My post was about  Brucep86's. His coach is the second line in my signature.

Re: No Power to Thermostat

Reply #11 –
Quote from: Brucep86 –
I guess I shouldn't be surprised since it is the original unit and is 27 years old.

I was going to suggest you get a Micro-Air Thermostat but I looked and they do not have one that works with the 4 button Dometic.  That 4 button thermostat works with the control boards in the AC units.  The problem could be in the front AC unit circuit board and not the Thermostat. 

Before thinking about replacing anything I would do what Joe's Post 5 suggests.  That is way cheaper then replacing or repairing.


Re: No Power to Thermostat

Reply #12 –
Quote from: turbojack –
,
No, 2014 IH45 has somewhat same system as the 1997 U295, no firefly in my coach on AC's.

My post was about  Brucep86's. His coach is the second line in my signature.

 ^.^d
 

Re: No Power to Thermostat

Reply #13 –
As Joe says in reply 5, remove the thermostat and check the RJ45 connection. To remove the thermostat take a fork and use a single tine to unlatch the catch at the bottom of the thermostat by sliding it right or left, I don't remember. Then Tilt it up and remove from wall mount. When you unplug the control wire make sure you don't let it slide into the wall or you will have a new problem.

Shoot some  contact cleaner into the connection and then plug and unplug it five or six times. Turn on thermostat. If it doesn't come on then go to your forward AC inside the coach and remove the filter cover and then take screws out  of the cover and remove it. Now you should see the other end of that control cable and do the same cleaning procedure. Plug in and check thermostat again. You could also by pass the cable in the wall with a test cable through the interior of coach. Power for the thermostat comes from that AC control board on the forward AC and runs through that cable.

My bad connection was control cable at AC unit.