Coleman T-stat problems
Hi, I have an RV with a Coleman thermostat set up. It controls our AC unit on the ceiling and our Suburban gas heater. Both appliances are ducted. The thermostat has HEAT, OFF, or COOL mode, and a HIGH, LOW, or FAN setting. It is not digital, it is old and it uses the little spiral metal thing that clicks back and forth to turn off the different functions when the temperature is appropriate. My problem is this: One day, I switched the thermostat to HEAT, and, after waiting a long time, the furnace never even tried to fire. I took the thermostat off the wall, inspected it, and noticed that a wire on the printed circuit board of the thermostat was burnt. It seemed as if there was a surge that blew the t-stat out, but our converter's fuse for the heater was still intact. Also, the AC still worked fine. I then replaced the thermostat. I bought a cheap White-Rodgers t-stat, that also had the little metal spiral actuator thing. This t-stat, however, did not have the right wire terminals. I tried hooking it up as best I could. When I switched it to heat, I smelled something burning, and what do you know, one of the wires on the back of the t-stat was burnt out. The AC function still worked fine. Now, getting really mad, I purchased a 100$ Coleman Mach thermostat, which does not have the little metal spring thing, but it does have the same wire terminals as the original did. I hooked it up, turned it to heat, and instantly a built-in fuse on the t-stat was burnt out. I went to RadioShack, picked up a box of fuses for it, put a new one in, and tried it again. It blew out immmediately. I did want to check the AC part of the t-stat, so I put a new fuse in and tried that. It worked fine for my AC unit. So there it is. Two replacement thermostats have been burnt out, but only when they are switched to heat. I had my furnace looked at, thinking there was maybe something wrong with it, but they said it was just fine. Could my problem be my converter? Or do I just need to get an actual Coleman thermostat (one with the spiral actuator thing) ? You say converter??? Just what is the power to the furnace and AC? Can you have two transformer there one for heat and one for cool? Most units have R for power W for heat Y for cool and G for fan. Does jumping R to W turn the furnace on??? ED I'll tell you what I know. There are 6 wires going to the thermostat: Red (Power) Blue (Ground) White (Heat) Yellow (AC Compressor) Gray (AC Fan) Green (AC Fan) All of these wires run on 12V DC. I do not have a battery hooked up to my camper, so the converter is what's sending the right/wrong amount of juice to the thermostat. I have tried to touch the red and white wires together, but that just makes my camper's 12 volt light fixtures dim. I don't remember the furnace ever making the lights dim when it's trying to fire. Check R and W just the wire for short Then check gas valve next. ED Like Edsays you're gonna have to trace out the W wire and check anything in it's circuit for a short with a multi meter. Bear with me, guys. I'm not an expert. What do you mean by trace it out? I've got a multimeter and I know use it, but I don't know what you mean. I have no idea where this wire goes, I assumed directly to the furnace's electronics board, but when I looked there there was no white wire. Also, there can't be a problem with the red power wire, right? The AC funtion still works fine, and the thermostat uses the red wire to send the power to the various AC wires. Trying to find out if you have a short on the W wire to the furnace are is it the controls at the furnace???? Like pull the W at the furnace then call for heat at the tstat. ED So, just to get this straight: You say I should pull the white wire from the furnace, turn the heat on at the thermostat, and take my multimeter and check to make sure the white wire at the furnace is the same voltage as the white wire at the thermostat? Or do I check for continuity between the red wire at the thermostat and the white wire at the furnace? Then what do I do from there? Sorry again if I am being too dumb. Just pull the R and W at the furnace now turn the tstat up on heat if the fuse is ok then its down in the furnace that you have to look see what power you read there on R and W this way ED Ed, I pulled the white and red wires from the furnace so they are not hooked up to it, and I called for heat on the tstat. Immediately the fuse blew. What does that mean? Id look first for a short in the tstat wire some where. ED just a heads up, the white wire is the heater (thermosensor) switch. It needs to be grounded to activate the heater. Look at the wire diagram on the furnace. Coleman thermostats are notorius for the heater (thermosensor) switch not carring enough amps to run suburban furnaces. I finally had to put in a relay to carry the furnace load. Basicly, the white wire energizes the coil on the relay and the contacts energize the furnace. White to one side of the coil and ground to the other side. Positive to one side of the contacts and furnace control, probably out side blue, connected the furnace mounted on off switch, the other contact is positive. roy@lonfu.com
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