Hello Sigforum friends. Now that we will actually have winter here in the Houston area, one of our two furnaces will not start( was working yesterday morning). The led error code suggests that the pressure switch is stuck open. I checked the tube and didn't find any obstruction.

Any thoughts? Bad pressure switch?

You have a forced air motor that starts then the vacuum from that will close the pressure switch. Make sure line from motor to switch is not split or blocked. I have seen the fitting on the motor that the line connects to get blocked so run something sharp down into the fittin on fan as well.

Took the flue/vent connection off, looks like a huge wasp nest had fallen down in there. Going to take the motor housing off to clean out remaining debris.

All clean, still no joy...

The orifice for the vacuum line on motor housing is very small. I use a very small drill bit and make sure it goes all the way down and touches the fan wheel. It can be very hard to get through. While vacuum is off motor housing suck on end like a straw should hear your sensor click

Pull the rubber hose off the inducer motor and very lightly suck and blow into the hose you should here it click this may luck out and get it started but pressure switch most likely gonna have to be replaced. If heat is needed immediately this is a one time fix if there are 2 wires going to the pressure switch pull them you will need to make a jumper put in one end of the pulled wires start furnace a couple seconds into put the jumper on the other wire this will run it until the stat is satisfied

Yeah, take the hose off of the pressure switch and suck and blow. This has worked every time I've tried it (3 times). I've replaced the pressure switch the next working day though.

Tried exactly what y'all describe. No luck. Figure either another obstruction up the flue, or bad pressure switch. Meh. Doesn't look like big box stores carry those switches.

As with any mechanical failure, we need to know what we're diagnosing (make/model)?

quote:

Originally posted by lee40215:
If heat is needed immediately this is a one time fix if there are 2 wires going to the pressure switch pull them you will need to make a jumper put in one end of the pulled wires start furnace a couple seconds into put the jumper on the other wire this will run it until the stat is satisfied

What you're suggesting is not only dangerous, but it could cause further harm to the equipment.

You don't go jumping around safeties without knowing if the safety is protecting you from a catastrophe.

Suggesting that a homeowner do something like this while not knowing:
* why its there in the first place
* how its protecting them and their equipment
* what may happen if its NOT bad and they bypass it
is reckless in so many ways.

quote:

Originally posted by Excam_Man:
As with any mechanical failure, we need to know what we're diagnosing (make/model)?

Luxaire GM8S040A12UH11B.

As with anything, the pressure switch may be bad.
However, since you had a wasp nest in the vent, I believe it *is* doing its job and protecting the equipment due to the lack of airflow through the venting system.

Assuming your vent motor (inducer) *is* running on a call for heat?

First, close the gas valve and turn off the gas control.
Pull the vent pipe and see if it blows air and still sets the pressure switch code.

If it doesn't, your vent is still plugged.

If it does, pull the inducer away from the back plate and test again.
If it still sets the code, you either have an obstruction from the inducer port to the pressure switch or a bad pressure switch.

quote:

Originally posted by tigereye313:

quote:

Originally posted by Excam_Man:
As with any mechanical failure, we need to know what we're diagnosing (make/model)?

Luxaire GM8S040A12UH11B.

Now that the starting point has been established!

quote:

Originally posted by Excam_Man:

quote:

Originally posted by lee40215:
If heat is needed immediately this is a one time fix if there are 2 wires going to the pressure switch pull them you will need to make a jumper put in one end of the pulled wires start furnace a couple seconds into put the jumper on the other wire this will run it until the stat is satisfied

What you're suggesting is not only dangerous, but it could cause further harm to the equipment.

You don't go jumping around safeties without knowing if the safety is protecting you from a catastrophe.

Sound advise from Excam Man

Last week of January one of our Central ACs stopped working. Yes I could have jury rigged the condenser and the air handler looked like new...but honestly after 15 years time to replace.

Good luck, never a good time for these pieces of equipment to die.

Any update?

quote:

Originally posted by Excam_Man:
Any update?

Thanks for checking back. It was a kaput induction motor. Couldn't have been the significantly less expensive pressure switch of course...

Inducers has been the big item this year, along with other 'failure to close pressure switch' issues.. Inducers can be a very high ticket item depending on age/manufacture.

*In your case, the switch was protecting you from a dangerous delayed ignition situation. As a non functioning inducer doesn't pull a draft through the heat exchanger for proper ignition.

Glad to hear its back in operation.

The part was the expensive part. The labor was very reasonable, especially with all the other climatological excitement here lately.

Maybe I can blend this discussion in with the HVAC guys here. I have a propane heater I use to heat the house. Noticed the flames had changed from a blue color to an orange. I had a repair rep come out and he looked things over and could nothing wrong. I had the gas company come out and they replaced a regulator but still change in flame color. I was told to replace the gas valve on the heater as the unit was 18 years old and the price of a new valve now is as much as I paid for this heater. Found the problem--- the humidifier was causing the problem. I turned the humidifier off and flames went back to blue. Live and Learn!!!