We're having issues with our forced draft gas fired furnace... Which was installed in 1990...

Whats happening is that occasionally when the thermostat calls for heat, is you can hear the furnace try to start up, but it wont start up even after 5-15 mins. The problem is solved when the thermostat is turned down a few degrees, then turned back up.

Any help? And if it needs to be replaced, whats a good one? Looking for a good price, and efficiency. Dont know what else to look for either.
TKs
~Nate

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95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

Well it's 19 years old. You may look at the ignitor plate and see if it's oxidized. If so, clean it VERY gently because these things are brittle and will break if you stare at them crooked.

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You don't need a weatherman to know which way the wind blows - Robert A. Zimmerman

Checked the viewing window, and the gas is burning when it's stuck in startup mode... It's just not blowing air occasionally.

Replacement most likely the cure?
~Nate

__________________
95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

No need to replace, it should be fixable. I believe there is something called a 'limit switch' which turns on the fan once the heat exchanger heats up to a certain temperature and keeps the fan running once the burners stop until the furnace cools down. It sounds as if the sensor or the switch itself is malfunctioning sometimes.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

as a temporary fix, set the fan switch to "ON" if it has one on the thermostat.

When I turn the fan switch to on, the fan does kick on. So i'm looking through the owners manual, and on the diagram I see what's called a pressure switch (normally closed), and pressure switch orifice... Is that where my problem lies or no?
~Nate

__________________
95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

How much gas is burning? Is it the pilot or the full flame? That makes a huge difference in your diagnosis.

Full flames, 4 rows of blue flames...

~Nate

__________________
95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

Then it's almost certainly the limit switch, as Kerry says. If it's mechanical (and it probably is), you can remove the cover and watch it turn as the furnace starts up.

Either the fan switch contacts are not working properly, or the friction is preventing the disk from turning. If it's the former, the limit switch will shut down the furnace before you get a fire. If it's the latter, well, maybe not.

In short, don't screw around with the limit switch. You might just want to get a new one. Good luck with that, because sometimes they are very hard to buy.

In what sense are they hard to buy?

When it works, the limit switch rotates, and when it clicks the blower comes on. Of course now that I've got a "please help me" thread up, it's been working fine all day... Unsure why the blower would not get the signal to turn on... Is there any other way to tell what else would cause the problem?

If the limit switch was not working properly, what would it do? Would it not rotate at all, or would it rotate and not engage the blower contacts?

tks
~Nate

__________________
95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

in general they cycle like this:

1 call for heat
2. draft fan starts (sensor checks to make sure draft fan is not over pressure) this is sensor 1 to check, will be on a flat round part that looks like 2 plates facing each other and crimped
3. igniter will light (skip if there is a gas pilot)
4. flame will light (there is a thermocouple to determine if flame is lit) this is the second sensor to check usually it just needs to be lightly steel wooled
5. large fan kicks on (this is next sensor to check) there will be an overtemp sensor somewhere near the big fan axle
6, there is also another overtemp sensor near the flame tubes.
7, all sensor should be closed and you should be able to read a low voltage through the sensor loop line. If one is open it will not show voltage, then you will have to work back through the series of sensors to find the open one.

one tip, the control PCB will have a flashing light telling you whats wrong and on the back of the PCB access door there should be a key to the flash counts. This will give you the starting point. I will bet you will have an open sensor (1 of the 4 is bad) or your flame sense thermocouple is dirty.

make sure you have a good filter as this will trigger overtemps if you dont have good airflow.

some os the overtemps are resetable, there is a button between the electric leads, but you will need to allow it to cool for it to reset, and you need to find what is causing it to trip.

aslo sometimes the big blower wont start, there may be a dead spot and it wont start. I have my fan running 24/7 in the winter because it has a dead spot and randomly doesnt start and pops the big fan overtemp sensor.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

Nice breakdown, in my experience with HE furnaces #2 is almost always the problem the pressure switch seems to be the weak link.

Correct me if I'm wrong but shouldn't his furnace have the flashing trouble lights on the board?

It could have diagnostic lights, however with it being a early 90's furnace and having what sounds like a Honeywell fan/limit control, I doubt it would. I believe you can purchase those at Home Depot or Lowes, but if you are unsure about anything, have someone who knows what they are doing install it. The limit setting must on the new control must match the manufacturers specification. If its set higher it could cause heat exchanger failure, fire, burn your house down, etc. Brand and model# of the furnace would help.

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'83 300D 198,000mi Howard
'03 Saturn Vue CVT 75,000mi(wifeys)

No LED's on anything, including the board on the right side on the interior of the furnace.

Heres the info that I have...
Deluxe energy saver
Forced Draft Upflow Gas Fired Furnace
Model number GUA 100 a016 ain
Serial Number R893600125
Thermostat t87f2873
Dealer Name, Switzer Electric


Any of that help?

~Nate

__________________
95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

if there is no trouble light you will need to use the voltmeter to find the bad sensor. I found your serial number listed under ICP Equipment as the maker, as stated earlier it has Honeywell parts. Once you find the open sensor you can find them on line pretty cheap, but also as stated, replace with the identical part. wouldnt want you burning down the house

__________________

1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)