I have a 1989 carrier furnace with problems

[chen]

model 58sx080-gg-1, I have problems with pilot assemblies before, this problem is probably a a pilot assembly, when I switch the furnace to heat, I don't now here the gas valve, kick in I have switched it on a nd off a few times then I hear the gas valve kick in I looked at the pilt kick in, but it doesn't light the burner and the blower doesn't kick in , checked the board that and the blower do work, what could it be thanks chen

[HayZee518]

the heater goes through a series of self checks before it starts. before the gas turns on the unit goes through a purge cycle. once this is done the gas valve for the pilot opens and the hot surface igniter attempts to fire up the pilot. if there is a flame a flame rod or cd cell verifies that there is a flame before the main gas valve opens. some factors come into play here. if your unit has a forced exhaust fan this may need to be operating and an air sail switch must make up before the main valve opens. no flame the unit goes into lockout. no exhaust air the unit goes into lockout. tell us what you have.

[chen]

my 1989 furnace

where on the internet can I download a manual for repairing or troubleshooting this furnace, this what my seems to do, the fan is auto, when I turn the thermostat to heat usually I could here a clunk thats is probably the gas valve opening for the pilot, I had done this a few times 1 of 3 I would here this, no heat, so went down to furnace, took off doors looked in at the pilot, pushed the interlock in, same thing 1out of 3, I would get the clunk, when the clunk was hear I would get a pilot and further clicking, waiting more than 5 minutes, it wouldn't lit the burners and turn the blower on, I have had problems before with the pilot assembly, I was told that dampness from humidity in the summer was causing this, I haven't had problems for 2 years since I tape the pipes outside shutoff, but again I have problems what do you recommend thanks

[HayZee518]

for a furnace that old 20 plus years I'd doubt you'd find any electrical diagram. dampness will play into the flame detect circuit just as if it were shorted to ground. is yours a standing pilot?

[hvacwiz]

You will need to change the 3 wire pilot assembly.

http://www.shop.com/carrier+3+wire+pilot?g=1&t=2&p=234073617&k=24

[chen]

1989 carrier

this furnace does have a pilot assembly, it does still click and do get a pilot but not getting it to lit the burners and bring in the blower, so it must be something in the electronics of the pilot assembly correct thanks

[HayZee518]

if there is a lit standing pilot then I would have to suspect the flame detector is also working. the flame detect generates a very small dc voltage that keeps the pilot valve open. my next area would be the wall thermostat not working or the transformer feeding the whole circuit.

[hvacwiz]

The 3wire pilot has a set of contacts in it, when the pilot heats up enough it switches over to anthor set of contacts, these contacts send 24v to your gas valve. Like i said if you change the pilot burner your problem should be solved. this is the most common replaced part on this furnace.

[hvacwiz]

if there is a lit standing pilot then I would have to suspect the flame detector is also working. the flame detect generates a very small dc voltage that keeps the pilot valve open. my next area would be the wall thermostat not working or the transformer feeding the whole circuit.

If the t-stat wasnt working he would not have a pilot at all. this furnace only lites the pilot on a call for heat.

[chen]

1989 furnace

thanks a lot guys it was my pilot assembly, I bought one never installed one before but it did everything as advertising, not that cold yet but took the chill out, I will refer back again for sure in spring my condensing unit outside just before it got cooler was making a noise and made the lights blink inside the house, it has to be either the compressor or the condensing fan motor, hoping it's just the fan thanks again

[chen]

that is the third one I put in 20 years

[hvacwiz]

Thats the usual lifespan for these, 5 to 7 years.

[SeattlePioneer]

Thats the usual lifespan for these, 5 to 7 years.

Hello Wiz----Personally, I've never found that Carrier pilot switches need to be replaced with any regularity. They may fail after years of use of course, but usually what's needed is to disassemble the pilot and clean the pilot orifice.I would have recommedned that in this instance, rather than replacing the pilot switch. I'd have figured a 95% probability that that would have solved the problem.

[HayZee518]

the pilot orifice is brass. the hole is very tiny, smaller than a pin point. by trying to clean it would increase the size of it making the pilot flame way too big. lng is one size lpg is another size. the pilot generator [flame detector] is a millivolt generator. it operates off the j-k thermopile principle - two dissimilar metals when heated generate a dc voltage 500-750 millivolt [thousanths of a volt] if the junction is open it won't generate a voltage. if the insulated wire inside is burnt it'll short out and the pilot valve will not stay open. the generator runs a very small electromagnetic valve pressing against a spring and internal orifice.

[SeattlePioneer]

Hello Hay,


Well, I've cleaned thousands of Carrier 3 wire pilot orifices in my twenty years as a repairman for a gas utility. 98% of the time they can be cleaned easily enough, the other 2% the remedy is to replace the orifice with a new one, unless the pilot switch itself is the problem. (which it is of course, occasionally).

But I'd certainly try cleaning or replacing the pilot orifice first rather than replacing the pilot assembly. Why replace something for $50-75 when you can clean it for ten minutes of your time?

Cleaning the pilot orifice every year or two will prevent this kind of furnace outage.