Heating problems

Mitch_4

but is the breaker and service switch on? sounds like you have no electricity to the unit.

Because you tried turning on the A/C, or put your thermostat fan switch to on..and the blower did not work electricity is not being supplied. It should do something..check the power supply. that is the only thing I can think of that will stop the furnace from doing ANYTHING.

Mitch

Tom_84

Heating & cooling not working

My furnace is not coming on. The burner does not come on, the fan does not come on, even in the "on" mode. Also, the AC does not work. Pilot is OK. Is there a schematic somewhere I can access for a generic central heating/cooling system?

Tom_84

thanks for the reply, mitch. yes, the power is reaching the service switch and the control transformer. but before i get up there with my voltmeter, it would be helpful if i had a schematic.

i've never had to troubleshoot one of these before, but i assume the transformer supplies 24vac to the thermostat which controls the gas valve and fan motor. i also know there's a temp switch in the plenum to delay the start of the fan until proper temp is reached. i would like to check voltages at the thermostat but i don't know what they should be on each wire.

Charles G.

Problem

As always, we need more information. Since you indicated presence of a pilot light, I'll assume an older design furnace, i.e. no draft inducer/circuit board/etc. Do you have 24 volts @ secondary of transformer? No wiring diagram inside blower compartment door? Rereading your post, I don't think you have enough understanding to realize what you're getting into. Best advice--put down the volt meter and pick up the telephone...

Tom_84

Well, thanks for the advice, Charles. But I think a Masters Degree in Electrical Engineering with over 30 years experience in design, troubleshooting, and accumulated knowledge, is adequate for this task. If I wanted to choose the easy way out by picking up the telephone, as you suggested, I would have done so. I prefer to solve my own problems.

Joannie_11

Get More Information

You shouldn't rely on something "generic" if you are going to put your hands inside a control box. Get the model number and serial number and contact the manufacturer for a schematic.

Empire_2

Easy Tom

If you have the knowledge, you should be able to follow the wires...... I don't think Charles meant anything bad to set you off, but while were on it, we try to help where ever possible. We didn't even get a brand name of the furnace. WHAT DO YOU WANT US TO DO NOW???? We need your advice.

Having said my piece, if you want to approach this again, Please see if there is any info on the inside panel or in the or on the furnace wall to the left or right of the Gas valve....Mod # or even a Logo that can help in identifying this unit.

Mike T.

Tim_33

Tom

How old is it? Make, model?

You may be able to find the information from the manufacturer of the unit or of the fan timer/control board. I know of no generic diagram, outside of the one in my head. As the others have mentioned, there's a good chance of a specific schematic being inside the unit or on the inside of an access panel.

I know the basic logic and sequence of operation of gas furnaces. Though, when delving into specifc faults, the generic info faoolwing may not apply.

If you don't have this info and want to do some basic trouble shooting, here's a start:

If the transformenr is working you'll have 120 vac on the primary coil and 24vac on the secondary coil. Output from the control transformer will be to the "R" terminal on the control board and should be providing 24vac to the same terminal at the t-stat.

On a "call for heat", the t-stat provides 24vac to the W output terminal and to the board.

When the fan switch is in the on position or when the unit is calling for heat/cool, there should be 24 vac at the G term.

On a call for cooling, the thermostat takes the 24 vac coming i on the R term and switches that signal to the Y terminal.

When nothing works, like you've described, I check, in this order; line voltage (power supply) to unit, transformer operation, thermostat operation/wiring. Usually don't get too far down this path before something shows up. Otherwise you need to find specific faults, safeties open, relays failed, etc.

Tom_84

Thanks, Tim, that is just the kind of help I was hoping for. In the mean time, however, I solved the problem. It seems I had an obstruction in the fan which was preventing air flow. A piece of cardboard from a filter had lodged in the squirrel cage and locked it up. Removing this solved the problem. No need for schematics in this one. Thanks for your help.

Mitch_4

Tom

Your solution is inconsistant with the symptoms in your original post, and there is no way that a piece of filter cardboard is going to stop a blower motor. I've seen ENTIRE filters in a blower wheel and it still ran albeit off balanace and noisy.

Do you have a door safety switch? Your original post says the unit did NOTHING, no burners etc..even if the blower was stuck, the burners would light, and the unit run until the high limit kicked it off.

If you have a door switch more likely you just reinstalled the door right, or your description of your problem was grossly inaccurate.

Everyone here is a great help, but the symptoms must be correct to help you.

Glad to hear you got heat.

Mitch