Ruud Silhouette 2 blower and inducer wont shut off unless power is killed

[mekanikman_402]

New member here. I have an old Ruud Silhouette 2 75,000 BTU 80% upflow gas furnace from 1995, and ever since yesterday the blower motor and inducer stay on after every heat cycle unless I turn the power off to the furnace and wait about 15 mins to turn it back on. If I turn the power back on any sooner than that, the blower and inducer instantly come on but the heat cycle will not start. But if I wait about 15 mins or so to turn the power back on then I can get the heat to run. I disconnected the 2 wires at the high limit switch and jumped them with no change. I haven't tried that with the roll out switch yet, but I did check it and it hasn't tripped. I also removed the thermostat faceplate and they both still run. But when I let it sit long enough and turn it back on it's fine. I can jump the thermostat wires and run the fan and inducer and they stop when I disconnect them. Also if I suck on the hose to the pressure switch it opens and closes. I did install a Honeywell touchscreen thermostat a few months ago along with new 18/8 wire, a new ignitor and gas valve. Everything has been working fine until yesterday. I just wonder if the thermostat is junk or if it's something in the control board. Filter is 1 week old, and I took the whole thing apart and cleaned it all about 2 weeks ago. I have a brand new Goodman 96% 2 stage furnace in my basement still in the box, just trying to save up some $$$ to have it installed. Please help!

 

[WorthFlorida]

It's hard to say but I would suspect the control board is the problem. Furnace fans usually will run after the flame goes out to suck out the remaining heat in the plenum to the living space. If the motor is switched off with relay the relay could be hanging up or the contacts are sticking together. It also could be the timer circuit is not timing out to open the relay.

At the thermostat just check that the fan is set to Automatic. When it is in the run mode when you think the fan should be off, disconnect the (usually) green wire (G terminal) at the furnace. This is the fan wire from the thermostat. If it shuts off the fan motor then it is the thermostat, if not then the problem is in the furnace control board.

FYI... All thermostats always have a setting (digital), a strap or switch for "electric heat" or "gas or oil heat". The difference is for the fan operation. For electric heating elements in a air handler, you want the fan to turn on immediately so there is no over heating of the space where the elements are. For gas or oil you want the fan to be delayed to give time to heat up the plenum so you're not blowing cold air and reducing the possibility of condensation in the plenum. Other than the old manual (analog) thermostats, most run the fan for about a minute after the heat is turned off. Most control boards in furnaces run the fan after the heat is switch off anyway for when old thermostats are used.

 

[Sponsor]

 

[mekanikman_402]

It's hard to say but I would suspect the control board is the problem. Furnace fans usually will run after the flame goes out to suck out the remaining heat in the plenum to the living space. If the motor is switched off with relay the relay could be hanging up or the contacts are sticking together. It also could be the timer circuit is not timing out to open the relay.

At the thermostat just check that the fan is set to Automatic. When it is in the run mode when you think the fan should be off, disconnect the (usually) green wire (G terminal) at the furnace. This is the fan wire from the thermostat. If it shuts off the fan motor then it is the thermostat, if not then the problem is in the furnace control board.

FYI... All thermostats always have a setting (digital), a strap or switch for "electric heat" or "gas or oil heat". The difference is for the fan operation. For electric heating elements in a air handler, you want the fan to turn on immediately so there is no over heating of the space where the elements are. For gas or oil you want the fan to be delayed to give time to heat up the plenum so you're not blowing cold air and reducing the possibility of condensation in the plenum. Other than the old manual (analog) thermostats, most run the fan for about a minute after the heat is turned off. Most control boards in furnaces run the fan after the heat is switch off anyway for when old thermostats are used.

It's the control board. One of the relays are sticking. I sprayed the board with break parts cleaner and now it works again like normal lol maybe it got inside the relays and unfroze them idk.