I have a 1989 carrier furnace with problems

[chen]

that is the third one I put in 20 years

[hvacwiz]

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

[SeattlePioneer]

Originally Posted by hvacwiz

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.

[HayZee518]

why do you call it a "pilot switch?" It isn't a switch! For a man with all that time in the field you should know proper terminology. A flame detector, a millivolt generator. Don't throw terms out there that a diy don't understand.

[SeattlePioneer]

Well, the SPDT switch in the Carrier pilot switch is one of it's major functions, as described by HVACWiz in an earlier post.

and there is no millivolt generator or thermocouple in it.

It sounds like this is a part and ignition system with which you aren't familiar.

[HayZee518]

I apologize there is a thing called a pilot switch - I checked the carrier distributorship.

[SeattlePioneer]

No problem Hay. It's an ignition system unique to a good many Carrier/Bryant/Payne/Day and Night brand furnaces roughly in the 1980s or so.

This ignition system replaced standing pilot lights and it was in turn replaced by the current hot surface ignition system.