HVAC Questions? Ask an HVAC Expert for Answers ASAP
Does this furnace have a standing pilot that you must manually light?
Does the ignitor glow bright orange?
This is a pressure switch issue.
First here is what I assume is your model. Please verify
Are you familiar with the pressure switch that must prove air flow?
Do you mind a hands on test?
Turn furnace off
Locate and remove the 2 wires connected to pressure switch and hold apart.
Turn power back on with thermostat turned to heat and up.
AFTER the exhaust fan starts, touch the 2 wires together so they make metal to metal contact. Some find a paper clip with the ends stuck into the bottom of the wire connectors helpful. If you do this do not let metal touch the cabinet. It is only 24v but could blow a fuse.
I need to know if the unit progresses after the pressure switch wires are touched together.
Thanks for your help....
Now there are a couple different circuit boards used in this unit. How many diagnostic lights are on your board?
and are you positive the code is 3? When the furnace was shut down and then restarted...did the diagnostic start solid or flashing....and then lock out with 3?
As I recall, the LED blinked 3 times rapidly, then I replaced the thermostat and now the LED blinks normally but slow. The light on the other furnace blinks normally, but fast. It runs normally, also.
Thanks...was the upper exhaust fan running during this time?
Take doors off furnace. Tape safety door switch down at top of bottom door. Locate where the thermostat wires attach to the circuit board. You should see R, Y, W, G, C.
Tell me if you have identified them and we will do another quick test. We are close to an answer now...
I noticed that this unit does not have a safety door switch. I looked for this on today and never located this door switch. Does every unit absolutely have a safety door switch? I may have overlooked it.
I see the R, Y, W, G, C on the circuit.
Before testing, should I reconnect the wires leading to the pressure switch?
page 7 figure 1 shows where a normally placed door switch would be.
Now..yes put wires back on pressure switch.
Turn power on....so at this point we have the circuit board exposed...power is on.
Now use a short wire, jumper etc...and jump R to W. One end of wire on R while other touching W...and hold in place....tell me if exhaust fan starts...and if it does if the unit tries to run..
Definitely no door switch present.
I jumped R and W with paperclip. The blower that lies encased behind the circuit board powers on, and the LED light flashes a steady, fast, "normal", RED. The blower at the top, above the pressure switch, does not come on at all. It has not ran during any of these procedures.
Note: In the past, it seemed that the when I turned on furnace from the thermostat, the blower behind the circuit board would come on but the LED would blink slow and steady, not fast. I may be incorrect.
Ok here is the issue at hand.
The reason you got the initial code 3 is because the exhaust fan did not start. Since it did not start the air switch could not be closed.
Now we are down to 2 choices....
1) the exhaust motor gets power but doesnt run
2) the exhaust fan does not get power which means circuit board is bad.
Now the exhaust motor could have power but not run due to obstruction in exhaust housing.
Try the R to W again...and this time spin the black fan wheel on the rear of the exhaust motor. This is a cooling fan for the exhaust motor. See if when you spin it if it tries to start ...is seized...if it hums... any sign of life. After this we would need a volt meter to see which is not working.
Just so that I am on the same page, you are referring to the exhaust motor that is displayed on page 19, figure 21, correct?
Good question...it could also be page 7 figure 2....It appears the unit could have either.
I am very sorry but I have to go offline. I will respond first thing tomorrow morning.
I hate to go offline this close to an answer for you, but I am out of time.
No heat. I think that the next step was to test something with a Multi-Meter, which I have. I am not at home presently. How long are you available today? I plan to return home in the next 3 hrs.
Send a response to this thread...I will be notified on my phone and I will respond as soon as I can.
Very sorry, had an emergency service call.
Which motor did you have ...the one with the cooling fan on back of motor or not?
I have one with the fan on the back of the motor. The fan moved freely when I jumped R and W.
So with R and W jumped...the fan did not run.....but spin by hand freely?
Yes, that is correct. No resistance from fan with R and W jumped.
There is a plug to the motor..it starts as wires from the circuit board and then there is a plastic connector....do you know what I refer to?
Yes, I am familiar with this connector. There is numbering on the connector for each connection.
Ok....we are at the point we need something to see if power is at that plug. A meter, a light tester, anything that can tell me if power is present...
set dial to ac volts ~
and set for range less than 600.
Test meter by sticking leads into a outlet you know works...look for 115 - 125 volts.
This will tell us if meter is set and working
Great....now unplug the motor and start the furnace....see if the plug that comes from the circuit board energizes with power or not.
Thank you....was it over 115 volts?
Ok, that is sufficient.
You have a bad exhaust fan motor. It may spin by hand but apparently has bad windings.
Looks like you will need to replace the inducer/exhaust motor.
OK. So I will need to simply replace the entire part seen on page 7, Figure 2 (Combustion Air Blower), correct? or will I need to open the item and remove the motor and replace that?
Nope the whole assembly. Which is really not a bad job. I believe you unhook the wiring and vent pipe...then 3 - 4 screws. Pretty quick job.
Thanks for all your help.