Ceiling exhaust fan runs intermitantly

[oldtymer]

I have a 2000 Monaco Dynasty with the kitchen ceiling exhaust fan that runs sometimes when I turn on the thermostat and will not run other times. I have not figured out any ryme or reason when the fan will work and when it will not. Currently it is not working and I traced the problem to low voltage (approximately 5-6 volts DC) at the supply wires to the thermostat. I also checked the fuse box and found 12 volts at the fuse (the fuse is labeled). In tracing the wires back from the thermostat, I found a multi wire plug connection under the false floor of the kitchen cabinet and the voltage here was also only 5-6 volts. This area is in the slide out of my Dynasty. From this point the wire goes behind the cabinets towards the ceiling. I am assuming somewhere between this point and the fuse panel that a bad connection is causing the low voltage but have no idea where to look. I am wondering if anyone else has run into this problem and possible may have some insight on where I should continue this investigation. I assume this circuit supplies more than the kitchen fan. Any help would be appreciated.

[bdpreece]

About the only way to find this is going to be by dropping any light fixtures and opening up any 12 volt receptacles between where you found the low voltage and the fuse panel where you say it checks ok. Most probably you have a wire nut connection which has vibrated loose over time. So far in chasing RV electrical wiring I have never come across a connection that was not made at an access point for some type of fixture. Be sure to reach up inside each opening as the wires may not be right over the holes. While you have all this open having someone move the wire at the previous hole will let you see if you are looking at the right wire. Is your fuse panel labeled fan or fans? Pull the fuse and see what else does not work. Could be as easy as the downstream connection at the bathroom fan. Good luck.

[oldtymer]

Thanks bdpreece for the sound advice. Pulling the fuse to identify other items on this circuit is a great idea. I will give this a try and let you know when I find the source of this problem.

[Robi.1014]

OT,
Let me take you down another troubleshooting path.

My thermostat caused me grief similar to what you're experiencing....and I found the following inside my thermostat. When set to OFF, there is a piece of plastic (a tab) that interrupts the voltage/current path out of the thermostat and into the fan. When the thermostat is set to a temp other than "OFF" , the absence of the plastic tab lets two pieces of metal make contact with each other. On mine, this "connection" was intermittent causing the fan to not run reliably.

[oldtymer]

Robi.1014, thanks This is good information to know. I am still trying to figure out why I do not have 12 volts to the thermostat. Once I get that issue solved, I will verify the thermostat is working properly. One new wrinkle is that I have discovered the light over the kitchen (dining?) table also does not have 12 volts and I am thinking this light may be on the same circuit. Thanks again for your insight on this vexing problem.

[bdpreece]

Just for giggles if you have some wire laying around, run a ground wire from a known good connection (battery ground would be nice) and take your readings again. A poor ground could also cause this problem.

[oldtymer]

bdpreece, I did check the ground at the multi pin connector by using this ground and testing all of the pins for voltage. I was able to get 12 volts on several pins just not the one that supplies the exhaust fan thermostat. This connector is in the slide out and following it back towards the fuse box, the wire bundle has a large loopl to allow the slide to move in and out and then goes up the back of the cabinet into the ceiling. Unfortunately the coil and wire going into the ceiling can be seen but is vertually inaccessable. I am still hunting potential connections in the ceiling at existing fixtures. I have eliminated the other two smaller fans since they are on a different circuit. Thanks again for your thoughts on the ground wire.

[bdpreece]

I used to use something similar to this at work Extech TG30 Wire Tracer and Tone Generator Kit | Electrical Testers | Instrumart

Wonder if you could rent one somewhere?

[oldtymer]

bdpreece, i actually have a signal tracer but have not used it on this problem. When I pulled the fuses to verify the circuit, i never found a fuse that eliminated the 5 volts that I am reading at the thermostat. I pulled all of the fuses one at a time. I do not want to try the signal tracer with voltage still reading in the wire. I am also not sure why the fuses do not eliminate the voltage, hopefully this curcuit was not rewired by the privious owner. My plan is to attempt to reach a point in the wire prior to the loop (for the slideout) and check the voltage, it could be that flexing of this wire bundle over time has caused the wire to break inside the insulation. Thanks for your help with this problem, I will let you know when I find a solution.

[Robi.1014]

When I can't find an easy way to test an electrical path or connection, I what-if alternate methods of troubleshooting. Here's another!!.....

Where you are currently reading 5VDC, take a long wire that is attached to a known-good 12VDC source and connect it to where you are reading 5VDC (the location where you believe that it should read 12VDC). Does the fan run correctly with this "new source" of juice?

[bdpreece]

Quote:

Originally Posted by oldtymer bdpreece, i actually have a signal tracer but have not used it on this problem. When I pulled the fuses to verify the circuit, i never found a fuse that eliminated the 5 volts that I am reading at the thermostat. I pulled all of the fuses one at a time. I do not want to try the signal tracer with voltage still reading in the wire. I am also not sure why the fuses do not eliminate the voltage, hopefully this curcuit was not rewired by the privious owner. My plan is to attempt to reach a point in the wire prior to the loop (for the slideout) and check the voltage, it could be that flexing of this wire bundle over time has caused the wire to break inside the insulation. Thanks for your help with this problem, I will let you know when I find a solution.

Don't know about your coach but I found on mine I have two sets of 12 volt fuses. One in the compartment under the drivers side front window, and the second hidden in the closet in the bedroom near the AC breaker panel. I have had the coach for almost a year and just found the ones in the closet by accident this trip as they are more or less hidden from view.

[oldtymer]

bdpreece

I took your advice and used a jumper wire at the multi-pin connection under the kitchen cabinet to introduce another 12 volt source. I found a 12 volt source in on another pin in this connector and connected this to the wire I thought supplied the fan. The fan and the light over the dining table both came on when the 12 volt jumper was introduced. This confirmed both that I had identified the correct wire and that the lack of 12 volts in this wire was the problem. Now to my supprise, when I removed the jumper the fan and light stayed on. I switched the fan on and off a few times and it appears to now be working. I suspect the source of the problem is likely a break in the wire near where it flexes to allow the slide out to move in and out, or corrosion in the multi-pin connector. while I was troubleshooting, I noticed the voltage in the fan wire would fluxuate slightly going from 5 to 8 volts when I moved the wire bundle around. I have no idea why the 12 volts was restored after I removed the jumper unles the when I shoved the jumper in the back of the multi-pin connector it created better continuity at this point in the circuit. Now that the fan is working, I have suspended my troubleshooting untill the problem recurs. Thanks for your help and ideas on this gremlin.

[bdpreece]

Odds are it will be back but at least now you know where to start looking.