Honeywell limit switch question

[Falcon67]

Any HVAC pros handy to answer a Q about a Honeywell fan/limit switch replacement? I've been living with one that's making me nuts by short cycling the blower. It seems to think the plenum temp can drop to 65F on a 80F day and shuts off the blower. I'm going to replace it, but the Honeywell unit seems to be more sensitive to temp changes than the older Cam-Stat unit. I found an H-Well unit that has a bimetal heater that will hold the fan on until the burners are signaled off, but would like to bounce the update off somebody before dropping $125+ on the part. The exiting item and the older unit are all obsolete. It's a Carrier furnace, vintage about 1976. Works great, but the blower is tired of all the on/off/on/off junk LOL.

 

[rburke65]

With a furnace that is 33+ years old, it would seem to me that you could not afford to run that furnace! Any idea on how efficient it might be? Just a thought.

 

[Falcon67]

It still runs good - not a big one, only 80K. It stays on a fairly cold setting since the wife hates heat. If we're in the living room, the heater is on about 66 and the little Dearborn is on low.

I ordered a timed unit to replace the control. Talked with a local Carrier service tech about it. I hate to take $$$ away from the pros, but the part plus service call here would have run about $400. I paid $98 including shipping. That's $50 less than the local supply house wanted for just the part. Even the tech said "It's just a switch."

If it make economic sense to re-fi the house once more to finish the kitchen and such this year or next, we would likely roll in a new unit. The AC part is a Rheem 10 SEER that is about 10 years old now. The furnace is an updraft unit in a tiny closet in the front bathroom and I'd much rather it be up in the attic on a platform. Easier to service up there. I could set the whole thing up then call the local pro to do the finish up, that'd save a big pile of bucks.

 

[chevelle67]

I was going to recommend going to a timed fan switch, sounds like you got it covered

 

[Falcon67]

Thanks. Took some digging on the Honeywell site to come up with a model number. It uses a bimetal heater to turn the fan on in about 60 seconds after the call for heat, holds it on until the call ends, then it'll shut down at the low limit as the exchanger cools off. Sounded good to me. Has a 200F upper safety shutoff which matches the max exchanger temp.