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My furnace fan won't stop running after the heating cycle is done. The only way to shut it down is to turn off the main power switch located near the furnace. I replaced the limit switch a while back (1-2 years ago) and things seemed to get better. Now it won't shut off at all. I've had it diagnosed twice. The most recent repair guy thought I have a short in the thermostat. When the fan is working properly it seems to have two speeds. If I turn the fan on manually at the thermostat, the fan runs on high. When it is running after a heating cycle (to cool the combustion chamber) it runs at a lower speed. I’m guessing the thermostat is not at fault because the fan is running at the low speed. I’m hoping to get a better idea if the thermostat is truly at fault before I replace it.
Furnace: RUUD, UGLD-08NE-GR
Thermostat: Carrier TSATCCPAC01-A
I also have an air conditioner located underneath the furnace.
Optional Information: Make : RUUD Model : UGLD-08NE-GRAlready Tried: replaced limit switch replaced filters
The heat and the air conditioning fan works differently on furnaces. The fan for air conditioning (and when you turn the fan switch to on) work through a fan relay. The heating fan either works through a fan-limit switch on the older units or through the circuit board on the newer units. Is the unit staying on in high speed all the time? Or is it just running for a while after the heat shuts off in low speed?
Did you put the correct one in? should have an 8 inch fan-limit with the heater in it. Should have a Ruud part #472054592.
Looks like the parts man sold me the right part. I have a L4064B2236 and it is 8" long.
Here's a picture of the dial. The fan off setting is well above our indoor temperature.
I turned it in both directions and the fan did not stop.
I pulled the red wire, fan load, off and sure enough the fan continued to run.
Is the fan relay easy to find? or is this not really a DIY project. I am happy to hire someone, I just haven't had much luck finding an experienced trouble shooter. Does it happen to show in any of these photos?
To be sure, it's this thing right? Does it need replacing? Is there anything else I can try? Thanks for all of your help so far.
I replaced the whole fan control and the problem is now slightly different. I probably have some wires mixed up. The original fan control was a Rheem 47-19807-01, see attached pictures. When rewiring, I substituted the brown wire (new control - the Honeywell from your link above) for the yellow wire (old control). Otherwise, everything is in the same place. Now when the thermostat is set to auto (for fan control) the fan runs continuously. If I switch the thermostat to on, the fan turns off completely (won't come on even when the limit switch hits the on temperature).
Right now I can:
The fan is running on low speed, when I turn the fan "on" using the thermostat, it runs on a higher speed. Could there be something wrong on the cooling side? Here is the wiring diagram for the furnace and fan control.
This is a downdraft furnace. I pulled the fan control relay and ohmed accross the red/black normally open contacts - it does show continuity. Does that mean the TDC contacts are stuck shut? Here's a picture of what I'm guessing is the TDC:
Here's the inside. I checked the continuity inside and there is continuity from red to red and from red to black.
Thanks for all your help - this was a really great experience. It is very satisfying to have the heater back up and running without the fan going all the time. Ruud wasn't very helpful in finding this part and neither were my local part stores. Hopefully I'll be able to track it down on the web.