[masraum]

OK, according to the directions

1 Thermostat calls for heat. Control module verifies that limit switches and pressure switch are in normally closed position

2 Draft inducer relay is energized. Draft induce motor starts and pressure switch normally open contacts close, energizing the gas control

3 Gas control provides power to igniter and pilot valve to light pilot. After proving pilot-flame, the main valve opens and igniter turns off

4 Control module energizes main blower in 75 seconds

5 After the thermostat is satisfied, gas control is de-energized. After a 5 socend post-purge, draft inducer de-energizes and returns pressure switch to normally closed position.

6 Main blower remains energized for 180 seconds.

NOTE: This furnace will lock-out if the main blower fails in heating mode. During lock-out, the control module's diagnostic light signal will be 4 flashes.

It's definitely not doing any flashes, 1, 2, 3 or 4. So that's good, I guess. The thing thinks it's working fine.

Originally Posted by Brian 162

The problem is the relay that brings on the motor which is on the circuit board is shot. You need to replace the circuit board.
If you have a multi-meter, cycle the furnace with no motor leads on the heating terminal on the circuit board. It should show 120 volts after 60-90 seconds. If no voltage is present after that time that tells me the board needs replacing.
You have proved by turning the fan on and changing speeds that the motor is fine.

I've got a couple of multimeters. I'll check to see if the terminal is getting power after 75 seconds.

Originally Posted by pete3799

There should be a temp. probe mounted on the hot air plenum. This is what turns the fan on automaticly when it reaches the preset temp. Mine has an auto/manual setting on it. Check that it's set on auto. If you take the cover off you should find it has two adjustments one for
on temp. and one for off temp. I think this is where your problem is. When the furnace kicks on and runs for a while the air heats the probe and when it reaches the preset temp. it turns the fan on. The fan should continue to run after the furnace has shut off untill the probe cools down to the cut out temp.

Hmm, I do see a part in the exploded diagram called the primary limit switch which looks like a temp probe that sticks into the furnace.


Thanks all.