For the last few days its been cold in my house, I went and check and found that the fan was running but no flames. I turned off the unit and when I started the unit the LED did the normal slow blink "no heat call" even when the thermostat was. I jumped the R and W in the control module and the blinking got faster and it started normally. The other way that it will run is if I switch emergency heat on. I pulled the cap of the thermostat and check for voltage B which for what I understand is common on Trane's had no voltage, Y had voltage when I checked in the relay box by the unit Y is hooked to a disc relay, the relay had a resistance of around 260 ohms in the switch side. The blue wires that comes from the thermostat, and the control module hooked up to a connection strip, then to the mentioned relay, before it got to the contact there all splice together. I took this apart and measure for voltage two of them had 24 volts but when they made contact to the wire that goes to the control module the reading goes to 0 volts. In normal operation the thermostat is showing aux heat every time it tries to start and in the relay box there is no power going to the W connection in the control module. I'm new at this and any help will be greatly appreciated.
The system runs on natural gas. The control module that it has is the White Rodgers 50A50-405. Like I mentioned before it runs just fine in emergency mode with the light in the control module doing the rapid blinking which indicates demand for heat. When running regularly it does not have a demand for heat, but the fan will run and the thermostat will have aux heat on "blue light".
The relay is a Therm-o-disc 12s10. Following the wiring from the blue wire that goes through it, and then to another big relay, it seems that this is the path to call for heat in the normal operating mode.
The blue wire that I've been referring too connects to the terminal C in the control module which has the thermostat word beside it. When this connection is made it suck the 24 volts out of the splice of four blue wires, which I believe 1 goes to the thermostat, one to the contact terminal, one to the outside unit and one to the control module. Not 100% sure.
The C terminal, is common. So if you disconnect it/them. And then read to the C terminal, you will bet a voltage reading. But once connected. You should not get a voltage reading.
With your thermostat configured to heat pump operation. It won't run the furnace on a call for heat until either the indoor set temp drops 2 or more degrees. And or the outdoor temp sensor or thermostat switches over to furnace.
What brand and model number is your outdoor unit.
Was the thermostat changed recently.
This is what I referred as the contact strip and in the upper left is the relay, as you can see the yellow wire goes trhough it I guess to energize it. In normal operation it has 24 volts in emergency mode has none. In the switch side it has the blue cable and like I explained before this wire has 0 volts so even if the relay is working nothing is on the wire to go through it.
The last picture is the control board for the furnace only. The first picture is a duel fuel control for the furnace and heat pump. Problem is the heat pump so go outside and start your diagnostic there.
I started my diagnostic outside by checking the fuses and there are good. The unit is humming like the compressor is rumming but the upper fan is not running. I got to do some disassembly to check the capacitor, what else should I check while I'm there.
I measure voltage in what I believe is the contactor and the capacitor, and it reads around 110 volts in the four connections in the contactor and the 3 connections of the capacitor.
The motor had a real loud squeal and I replaced it last summer, it was recommended to change the capacitor too but at the time the capacitor was not much more than a year old so I didn't. Thank you everyone for your help I will let you know how the new capacitor does.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
DIY Home Improvement Forum
3.1M posts
319.6K members
Since 2003
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!