I have a thermostat that is completely blank (no display). I'd like to troubleshoot it myself even if I do ultimately hire a pro! We're in sunny southern california, so it's possible it's had no display for sometime, but when I first noticed it was after we flipped all circuit breakers to the house for another reason (checking power consumption). I'm ignorant of heating systems, but having done research, it seems that one of two things are most likely:
1. No power to main unit. Main unit communicates to thermostat via 24 V or lower.
2. Power to main unit, but no power from main unit to thermostat. Possibly bad connections, etc.
I'd like some ideas from a kind and patient soul on how to troubleshoot both of these.
Starting with #1…. The main heater is plugged in, but how the heck does one tell "it's on"? I see no lights, etc to indicate it is on. I have tried the socket it's plugged into and it's powered. However perhaps there is an on/off switch? The model # is MPGA075B4B. Originally, I thought the make was Honeywell because I saw that huge name on the on/off gas switch in the unit. But as I did internet searches, the name "Ducane" kept popping up. Not sure if these heaters are made by one company and use Honeywell switch or what is going on. Anyhow, I can't find a manual for it, and I can't see how to know if it's "on".
Number 1 seems like where I should start. Assuming the unit is on, my understanding is that one can check at the thermostat if it's even getting power.
a) How does one do this?
b) assuming it is not, what next? Do you check the Honeywell switch on the heating unit itself?
The Thermostat in the living room (that is blank) is Venter, Model T1050. There are 4 wires coming out. Red, Green, W1, and C (which looks blue to me!).
Finally, any other ideas? And I can post photos or more information.
I appreciate the help.
Dave
Best Answer
Since you have a multi-meter, you can check the voltage of the wires at the thermostat. Make sure the meter is set to AC (Alternating Current) in this case, and if there are ranges, something safe for 24v. Probe the Red and Blue wires and see if there is 24v. You can also check the voltage between the red and any other wire.
If there is no voltage, the low-voltage power supply for the furnace is bad or not getting any power. There is probably a breaker in the main cabinet for the furnace, but there will probably be a breaker located on the furnace/air handler as well. Make sure they are both on and recheck the voltage.
The power supply will typically look like this and should have two 120v wires and two 24v wires coming off of it.
If you can find it, check the voltage going to it to see if 120v is present. Troubleshooting will move on from here if there is not 120v.
Thermostat information
Assuming the wire colors you have are standard...
To turn on the fan, the thermostat makes a connection between the red and green wires. If you place a jumper between these wires, the fan should run.
To turn on the heat a connection is made between the red and white wires. The call for heat will always be accompanied by the call for fan.
The blue wire doesn't signal anything - it just supplies voltage to the thermostat in conjunction with the red wire. To draw a parallel with your house wiring, the red wire is like the black "hot" wire, and blue is like the white "common" wire.