Gas and Oil Home Heating Furnaces - carrier furnace, blower stays on, heat and ac both still work

i have a 58dh series carrier that has a manufacture date of 1982. still heats no problem, but the blower fan stays on constantly unless i flip the switch next to the furnace to turn everything off. i have a honeywell thermostat digital. i remove the thermostat and the blower still stays on. i disconnect the wire at the furnace that goes to G and it still stays on. i looked at the control board and it has a transformer that was capped off and a newer transformer that is wired in, the transformer was before i even bought the house it is a uet-105 transformer. any help would be appreciated!!

The control board may be bad.

should i install a new transformer with a new board?

Not necessarily. Make sure the board is the problem first. That's just one possibility.

any other suggestions to check on this before ordering a board?

The probability that the circuit board is bad is low.

You need to check the low voltage control circuit to see at what point the 24 VAC power is being stopped. That could be a bad transformer, open fusible link, open high temperature limit switch or open draft limit switch. More than like, one of these controls is open, any of which will cause the fan to run constantly.

This is my 1st time here so I may do this wrong.
I dont know what your furnace looks like or the board, but I would think the fan relay is stuck, it is energized by G
but the contacts are on the 120 volt side giving the blower motor power all the time if the contacts are stuck in the closed position (aka the blower turns off when you flip the 120 volt switch off). The fan relay my be the color brown with 6 wires pluged into it but of course I cant see it and there are so many variations of the same thing out there this also assumes the furnace has a fan switch.

Are we sure it has a board, this is 1982 we are talking about. You may have a camstat or honeywell fan/limit combo I would guess the former but anyway you need to eliminate some possibilities before you buy any parts. Disconnect the green wire where it enters the furnace then turn the furnace back on. If the fan still runs you have eliminated the thermostat and all the wiring as a cause. Now concentrate on whatever controls the fan. Possibilities are a heated or timed fan relay as previously listed and if it has one, a board.

http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/58dh-2p.pdf


Like a lot of Carrier/BDP furnaces at the time, this furnace runs the fan continuously anytime the 24 VAC power fails or is interrupted by an open safety switch.

On a furnace of this type, checking that circuit is the obvious first thing to do when that symptom appears.

Ok if all are correct GET A NEW BOARD # CES011057-02 could cost up to $ 310.00.
That is if all information is correct. If your old board has the large black relays most likely the problem is the fan relay is stuck.
Call your local Carrier dealer and get one you can do it.

darryl

Well, dorcraft, I'd estimate that there is less than a 1% probability that a new circuit board will solve the problem, and a 90% probability that the problem is in an open safety circuit or defect with the 24 VAC circuit as I described earlier.

So you'd have to replace about a hundred circuit boards for a cost of $30,000 based on your suggested price before you found a furnace with this problem where replcing the circuit board would solve the problem.

Do you know anything about the furnace described in the opening post or is your suggestion pure guesswork?

Ok , 03XB9r said "still heating" this wipes out an open limit on this unit.. will not heat with an open circuit.. this unit does use a control board on it just like the ones on the 58GP or the old 394GAD and as on those units if the furnace is still heating and the board has no call for fan you will find that one of the large relays on the board (if it has been replaced,, small relay) is for the fan and it is stuck... there are several companies now making a generic board for this unit or you can go back to carrier for and OEM board.



and.....
Well, dorcraft, I'd estimate that there is less than a 1% probability that a new circuit board will solve the problem, and a 90% probability that the problem is in an open safety circuit or defect with the 24 VAC circuit as I described earlier.

So you'd have to replace about a hundred circuit boards for a cost of $30,000 based on your suggested price before you found a furnace with this problem where replcing the circuit board would solve the problem.

Do you know anything about the furnace described in the opening post or is your suggestion pure guesswork?

I just wonder why we all cant get along.... been on these boards a week now and see way to much of this......

and yes SeattlePioneer is correct if a limit is open this unit will run the fan all the time.. but it will not still heat with an open limit.......

Ok , 03XB9r said "still heating" this wipes out an open limit on this unit.. will not heat with an open circuitand yes SeattlePioneer is correct if a limit is open this unit will run the fan all the time.. but it will not still heat with an open limit.......


Yes, you and dorcraft are correct and I was wrong. I missed the fact that the furnace was still heating.

Thanks for pointing out my error so I could see where my reasoning was wrong.

well just to update everyone. i changed the circuit board with the icm275. and it fixed my problem. everything works like it should again.


thanks