Thermostat problem

[Robert Mathis]

The rears thermostat in our coach just went blank, and the rear and mid a/c's will not work.  I can unplug it and when I plug it back in, the display will come alive for about a minute then go blank again.  Do any of you know any way to jump start the system, or do I need to get a new thermostat?  I tried swapping the front to the back and it stays lit back there, and the rear one does the same "blanking" when plugged in to the front system.

[Gerald Farris]

Robert,
From your description, unfortunately it sounds like you need a new thermostat.

Gerald

[Robert Mathis]

I came to the same conclusion and just ordered one on line. The bad thing is that the coach is 150 miles from home, and we are just coming over here on the weekends.  So, I guess the front a/c will be running full time for the next week.

[Robert Mathis]

And as soon as I ordered the new one, and plugged the old one back in, it started working and the rear airs came on. I don't know what I did, but I'm happy.

[Edward Buker]

It responded out of fear.... :-) It could be some oxidation on a contact point or a connection/wire that was reseated more firmly and now conducts. Sometimes logic in an IC will get a stuck fault and dropping power completely for some period of time can discharge the errant device and allow operation again. Either of these issues can return so having a spare would be a good back up for you.

Later Ed

[Robert Mathis]

Yes, it quit working again shortly after the post and would not resume operation. I think it must be the micro-processor because the little zone numbers stay lit and everything else goes dark.

[Edward Buker]

One last thing that you can check... See if you can inspect the solder joints on the board. Take a magnifying glass and look around each component solder joint. Sometimes the higher current paths will get electromigration where the solder over time will void and crack around the joint. The fact that it is intermittent could mean that it may just be a solder or land issue.  If it is that type problem, with a light soldering iron and a quick heating and soldering they can usually be repaired.

More than likely it is a failed component but sometimes you can get lucky....

Later Ed

[Robert Mathis]

Thanks, Ed, but we left it in Steinhatchee and came home for the week to work. I hope the new one gets in before the weekend. When I unplug it and plug it back in, it stay on for almost a minute then dies out again. If the new one doesn't get here in time, I'll give your suggestion a try next weekend. We are about three hours away from the coach now, at home on the East Coast of Florida, but will go back over every weekend thru August to dive for Scallops in the Gulf of Mexico. I was toyying with the idea of running down to Alliance and getting a replacement if they have one.

[Robert Mathis]

Update on our thermostat problem. The new one was delivered yesterday, and we just got to the campground in Steinhatchee. When I went back to the bedroom to install the new one, I found it to be 72 degrees back there, both rear a/c's running strong and the old thermostat working like always. I'm now totally stumped, but I now have a spare.

[Edward Buker]

It is an intermittent fail due to a bad device or contact. They are hard to diagnose as to the root cause. One thing you know is that the thermostat has failed three times or more in a relatively short period of time. If you change it out and you do not get a fail in several weeks then you know that the problem is resolved with the thermostat change. These type fails do not typically fix themselves for very long so I would just replace it and have piece of mind that you have a system that you can now trust. Intermittent electronic component fails are quite common with multiple possible causes so you are not really stumped here, you are in limbo just waiting for the next fail.

Later Ed

[Robert Mathis]

Ed, I certainly agree with you about the nature of intermittent fails. I chased an engine problem in an S10 Balzer for almost a year before we could actually get it to a computer while it was failing. I am going to install the new thermostat and see how that goes.

[Robert Mathis]

Well, it failed again Sunday afternoon, and I replced the old thermostat with the brand new one.  Guess what, it didn't work either.  I tried to program it, and got an error message.  I traced out the wiring, and could find nothing wrong. Based on information I got off the internet, I unplugged the wire from the middle unit to rear unit connection and tried hooking the theremostat up there, but no joy.  I finally gave up and got ready to come home, then it started working again.  I am giving up and taking it to Alliance next week.  I am beginning to suspect there is a problem with the control boards, and I don't have the expertice to tackle that.

[Edward Buker]

Bob,

The front thermostat in your first post seemed to work in the back. If so you could leave it there and try the new one in the front. You may have just gotten a defective unit. You know that a good thermostat will operate in the front position, so that is a good place to also test the new thermostat. If this swap does not help sort things out then head to Alliance.

Later Ed

[Robert Mathis]

I may try that when we go back over Friday. This is our last weekend over there, so we will be bringing the rig home Sunday anyway. These intermittent problems are always hard to diagnose. I also thought about trying the new thermostat when the old one is working to see if it will program, but trying it in the front is a good idea.

[Bill Stireman]

I had a similar problem and when we inspected the telephone type connector in the tank bay we found corrosion.  Cleaned the connector and had no more problem.

Bill Stireman
'04 Monterey Laguna
400 HP Cat C9