Imo new at this service and I can't get a hold of my super. Please help!! Unit called for heat furnaces fire off and when the room is satisfied burners shut down and the blower keeps running. I checked the role out, hi limit, safety at the blower and even changed the circuit board. Is there anything else to check?

Thermostat fan selector switch- set to on or auto? Maybe a stuck time-delay stack switch-give the unit a good thump near the control compartment, see if blower stops.

I even disconnected the red and green at the t-stat... even gave the relays a good thump.

Stuck blower relay of some sort

Can u elaborate a little more if possible

Sure. Trace down the blower relay in the furnace circuit. Then test the relay to see if the contacts are welded shut causing the blower to run all the time.

You might also check for a shorted thermostat wire causing G to be activated all the time. Test by removing the G=Green wire off the circuit board terminal and see if the blower keeps running.

If I remove all t stat wires from the board and the blower keeps running then is that 100 percent that the circuit board with the relay is bad?

Find the part number from the circuit board. It might start with "HH84AA..."-

If the transformer is bad on this furnace the blower will run until the power is shut off.

So do you get any response when you turn the fan to the on position or if you turn the A C on, if not still a indication that the transformer is bad.

Quote:

---

Originally Posted by pauly2121

Imo new at this service and i can't get a hold of my super. please help!!! unit called for heat furnaces fire off and when the room is satisfied burners shut down and the blower keeps running. i checked the role out, hi limit, safety at the blower and even changed the circuit board. is there anything else to check?

---

If the heating still works, the transformer must be OK. Some of these units use a normally closed relay for blower control, and the relay is powered to turn the blower off. Failure of the timing circuit on certain boards will result in continuous fan, while the other control functions of the board are maintained. Did you replace the board with new or used?

With thermostat wires off \ disconnected from circuit board take a volt meter and test between red and white - if you get 24 volt reading heat is off and you have stuck relay in circuit board. If you get a reading of 0 volts with t stat wires off circuit board then change board that's the only option to make it work. Once you pull off circuit board look at back side for burnt spots- look front side for burnt diaods and browning around circuits - this is just for you own info

L

Quote:

---

Originally Posted by altonbee

with thermostat wires off \ disconnected from circuit board take a volt meter and test between red and white - if you get 24 volt reading heat is off and you have stuck relay in circuit board. If you get a reading of 0 volts with t stat wires off circuit board then change board thats the only option to make it work. Once you pull off circuit board look at back side for burnt spots- look front side for burnt diaods and browning around circuits - this is just for you own info

---

This post is 4 years old! Look at the original posting date. But, thanks for helping.