Yesterday my furnace worked. Today, it won't do anything, nor will my AC nor the fan. Nothing responds to the thermostat control. I checked the gas and it's plentiful. I checked the breakers and fuses in the panel. All are good. I changed the 20A for the AC circuit just in case. I took the fuse out of the thermostat and put it in my neighbours thermostat and his works with it. I flipped the reset button numerous times on the furnace. I turned off the shore power and ran it on just battery to make sure it wasn't dead. All good. I pulled the wires out of the wall just in case there was an in line fuse behind the thermostat. Nothing there. I checked the rooftop unit just in case of critter invasion etc. I checked over the circuit board of the thermostat and everything looks normal. Any ideas???
Odds are there is no 12 volts at the thermostat since multiple items are not working. If this is a digital thermostat it should display the temp when it receives power. You didn't mention the type of thermostat or whether it displayed anything.
The thermostat is really nothing more than a switch. Depending on the function you select it simply connects 12 volts to a wire that feeds the item you want to turn on. 12 volts connected to the furnace line will turn it on. 12 volts connected to the AC fan will turn that on. 12 volts connected to the AC compressor will turn that on.
You can jumper the 12 volts to any of these lines to get the appliance to turn on. I have included a picture of a typical thermostat's wire connections. You can't rely on colors as it depends on what Jayco decided to use at the time.
If this is a digital thermostat and it doesn't light, an open ground would also cause it to not work.
__________________
Jim
Retired electronic technician (45 years in the field)
2017 Greyhawk 29W (solar & many other mods)
wife (maybe I should have given her top billing)
There is no voltage at the thermostat. Any thoughts on next step?
Check the battery first, then the fuse for the circuit the thermostat is on. Also check to see if there is a fuse in line with the thermostat behind the wall. With a volt meter you can disconnect the positive terminal of the battery to see if there is power from your converter to the battery. Connect the lead that was on the positive terminal to one lead of your volt meter and touch the other lead to the negative terminal.
Your question on which setting to use on the voltmeter indicates you are not familiar with using one which is fine. Until you actually have to use a meter it can indeed be a mystery. I have attached some docs that will get you going on using the meter and basic RV system troubleshooting. Don't feel bad about not knowing the meter as everyone has to start from square one at some point.
As far as where the 12 volt power comes from for the thermostat, it will definitely come from the power distribution panel a.k.a. fuse panel. The system you are troubleshooting is 12 volt which is the power used to control RV items. The furnace is 100% 12 volts, the AC uses 12 volts to control it and 120 volts to run the motors (fan and compressor). Ignore the 120 volts as your problem is in the 12 volt side of things.
Look at your fuse box and see if anything is labelled thermostat. I doubt that there will be one but you never know. If there isn't one, look for one labelled Furnace. It is very possible that the thermostat 12 volts is coming from the furnace. The 12 volts at the panel could be fed to the furnace where it would be tapped off and then fed to the thermostat. Once at the thermostat it would then be fed back down to the furnace to turn it on.
Feeding the thermostat its 12 volts from the furnace just simplifies the wiring of things. It is easier to feed it this way rather than run a dedicated single wire from the fuse panel to the thermostat.
Anyway, pull the fuse that feeds the furnace and test it with your meter using the resistance setting. Just looking at the fuse does not guarantee 100% that it is good. I describe how to test a fuse in the attached Quick Multimeter Instructions document. The more you play with the test meter the more comfortable you will be using it. Also, just pulling and reinserting the fuse may solve your problem if it had a poor connection.
If the fuse is good and there is no separate fuse for the thermostat, you may have a problem that is beyond easy troubleshooting. If your furnace is easy to access (most are not) you could measure for 12 volts there.
Good luck! Troubleshooting these things can be intimidating but once you get a feel for it, it should become easier. This doesn't guarantee you will be able to find and fix the problem. But you will be at least able to give it your best shot.
__________________
Jim
Retired electronic technician (45 years in the field)
2017 Greyhawk 29W (solar & many other mods)
wife (maybe I should have given her top billing)
Thank you. My problem is I don't understand electrical systems and know where to go to find the cause of an issue, especially with this trailer. It's the first electrical issue it's had so I'm troubleshooting for sure to find the cause but learning how it is designed as I go. I am familiar with a multimeter, just didn't read your post closely enough the first time before I responded to know what it was I was looking for. My bad. I was also freezing. When I left the house in my shorts and t-shirt it was 34celcius but when I got to the park, only 45 minutes away, it was freezing cold. So I was hurrying to get it solved. Welcome to New Brunswick! And to top it all off, I brought my damn clamp meter and not my multi. It has limited settings and doesn't give very precise readings. Anyway, your sheet is great info and I appreciate it. I'll learn much from it. I tested the continuity on all the involved fuses and they are all good. Funny thing is, the damn furnace worked fine Thursday to Sunday and then quit, along with everything associated with the thermostat. It is very accessible so I may yank it out and take the shell off it to see if anything is out of order. But I'm going to test the power at the unit first, to try to isolate where it's going awry. I am grateful for all the help.
My ac and heat also not working. Found that thermal breaker mounted to furnace also supplies 12 volts to thermostat. Mine was only sending 2-3 volts on the load side of the switch to the thermostat. That explained why neither system was working. I replaced the breaker/ switch and it worked again for one week. Again I only had a few volts coming from the thermal switch. I assume they’re cheap junk and I will now eliminate. I’m going to bypass and add a non fused switch ahead of the furnace. From there I will add a fuse-able link to the furnace with a slow blow 10-amp fuse. I will also add another fuseable link for the thermostat power but use a fast acting 10-amp since this is only for control wiring.
Yesterday my furnace worked. Today, it won't do anything, nor will my AC nor the fan. Nothing responds to the thermostat control. I checked the gas and it's plentiful. I checked the breakers and fuses in the panel. All are good. I changed the 20A for the AC circuit just in case. I took the fuse out of the thermostat and put it in my neighbours thermostat and his works with it. I flipped the reset button numerous times on the furnace. I turned off the shore power and ran it on just battery to make sure it wasn't dead. All good. I pulled the wires out of the wall just in case there was an in line fuse behind the thermostat. Nothing there. I checked the rooftop unit just in case of critter invasion etc. I checked over the circuit board of the thermostat and everything looks normal. Any ideas???
Just found this post on Google. I'm having the same exact issues. Were you ever able to fix it?
Linear Mode
