rudd blower

my rudd furnace blower runs continously (dont know model) but must be 15 years old or more. Had plumbers working today on basement bathroom near unit sweating pipes and vacumming up cement dust that was around when they buried plumbing in concrete slab. I replaced the filter and it was caked with stuff. I banged on the unit and it still ran. I removed filter and still runs. The heat does come on and off. the thermostat is set to auto. when i open thermostat and remove only the green wire from its contact point the blower goes off. is that enough proof that it is thermostat or might the problem lie elsewhere? THANKS.

 

pbarra:

Is it possible the fan switch, if there is one, is set to continuous?

 

the only fan switch i see i on the thermostat. there is not one on furnace - could there be one inside the furnace?

 

when i connect the green and yellow wires that go to the thermostat the blower runs. is there something in the thermostat that turns the blower on and off or something in the furnace that does that or both. as i slide the fan switch on thermostat back and forth from auto to on i hear the blower make a sound. it continues to run but there is sudden sound that it makes for a second as i slide switch.

 

In cooling mode the thermostat starts the fan. In heating mode, a time-delay or a temperature switch does it. You should look for the fan control and thats most likely your problem. It will be inside the furnace cabinet somewhere.

 

once i find the fan control how do i diagnose it? what does it look like? how do i recognize the fan control as the fan control/ THANKS. Could the filter not replaced for months being really dirty have created a problem?

 

You didnt say what you have for heat That I see. Is it gas, oil, heatpump or electric? . You say longtime bad filter. Is the AC coil clean? You can also have a relay in the unit that goes from high to low on the fan for heat to cool also. You said it makes noise when you go to fan on. What ever it is look at the schematic there on the door and look what you have or where the relay or fan control is. Then we can help you. ED

 

i have a gas forced air unit. I expect my coils are dirty - how do i access them. I took off the panel covering the burners (which turned off blower) and banged on a silver rectangular box that said honeywell and reinstalled panel and turned on unit from thermostat and the blower was off. i will check the schematic

 

On top of your gas furnace should be the A coil for the A/C sometimes you can unscrew the covers there and see the underside of the coil.See if you can see a light through the coil. It sounds like that small box you banged on is the fan on off control and was stuck on. The points burn sometimes and do that. Or it can still be the fan relay for heat and coll .Look at the schematic for sur and find out. ED

 

The silver Honeywell box was your fan & limit control. It is the source of the problem. You will need to know what length the probe is. The best way to get the right one is to take the old one along when you go to get the new one. It is an L4046 but the last 4 digits tell what length the probe is and OEM can be anything but the replacements are either 5 or 11 inches.