Fan blower only works on high speed....

[murraymcleod]

I have the Itasca detailed below, and lately has developed an issue where the dash fan will only work on the high (noisy!) switch setting. After starting the engine (Chevy workhorse 8.1 engine chassis) it sometimes will work on the lower settings, but after five to ten minutes it shuts off and will only blow on the high setting. It's the same whether on vent or on AC mode. Is this a fan problem, or a switch problem? Thanks.

[AstroRig57]

Incredibly enough, and this may sound counter-intuitive, but I had a bad ground where it connects into the blower motor behave in the same manner. I trouble shot the system all the way from the resistor, to the relay, to the switch with no definitive diagnosis.

The next step was to backprobe from the motor. I removed the panel/vent assembly from the passengers side to get to the motor, and since it happened to be after dark, I noticed arcing as the motor cut in and out, low to high... The motor ground was held on only with a small sheet metal screw mounted to the motor/blower chassis. When I tightened the screw everything worked properly...and at all speeds. After a few off/on cycles, the blower motor stopped working or would work only on high. The screw had so few threads in contact that it had backed itself out and would not tighten. I speculate that it would sometimes work on high only because the higher voltage bridged the gap at the bad ground contact. (thus the arcing)

I removed the blower/motor assembly, filed the paint from the area around where the ground screw mounted, and installed a bolt with a lock washer and nut into the hole. When I reassembled the blower/motor assembly I attached the ground to the bolt with a lock washer and nut. I have not had an issue since.

[murraymcleod]

We went on a short trip this past week, and lo and behold the fan seemed to work just fine. All speeds worked as they are supposed to. Of course this was right after I had orderd a new dash fan switch!

So now I have an extra resistor assembly and fan switch for when the problems start again....the only thing I can think of that might have fixed the problem is that I pulled the wire harness off the switch while trouble shooting and maybe I improved the connection when putting things back to normal to go on our trip. It was difficult to get the harness back on so I used some electrical (light bulb) grease to help.

[murraymcleod]

OK...I tried a new resistor assembly, and that did not fix the problem. As I note above, it seems that there was voltage to the resistor regardless of the switch position, but I've gone ahead and ordered a new switch....hopefully that will do it!

(Anyone know why the "Subscribe and send email..." option isn't working for me?)

[AstroRig57]

FWIW...this is a part of the directions I used, from my Ford Expedition service manual, to to troubleshoot my RV blower problems.

I can't tell you, because I can't remember, which pin on the RV blower motor resistor block corresponds to which in the manual and I'm certainly not going to pull mine out to figure it out.

There's also a section on troubleshooting the relay and switch.

[murraymcleod]

fourmat wrote:
with your fan switch in the lower settings do you have 12V to the resistor if you do then replace the resistor if you don't then it is the fan switch or wiring.

The fan switch seemed to provide 12v to the resistors no matter which setting it was on. I think I'll just replace the resistor assembly first as they are not that expensive ($12 vs $40 for the switch!). The black spot on the switch did NOT appear to be a burned area, but just grease or some fastening material.
Thanks to all for the help....I'll let you know the outcome!

[azrving]

Looking more closely at the switch. What is the small dark spot in the center? Is it burned right there or is it just grease or something?

[Harvard]

From the picture it appears that the thermal fuse is the component that has over heated and failed open (like it was designed to do if the area gets too hot). The thermal fuse is that small cylinder shaped device. JMO

[azrving]

Your resistor doesn't "look" bad and the heat marks on the coil are normal as it's burning off energy instead of spinning the blower fast. You need to find the schematic or diagram for your chassis.

Do any of these look like your system
these?

[azrving]

Don't replace anything until you prove what is wrong. This may help to further troubleshoot. Notice in this video that there are 2 relays. Not that it's exactly your system. just one example.

[fourmat]

with your fan switch in the lower settings do you have 12V to the resistor if you do then replace the resistor if you don't then it is the fan switch or wiring.

[murraymcleod]

The thermistor is the resistor like thing below the coil? And that's a high temp cut-off or something? It seemed as though, from my voltage test, that current was passing through this assembly ok regardless of where the switch was set, but does that mean the fan should be powered in these situations?

So you would recommend replacing this resistor assembly first, as it looks suspect?

[AstroRig57]

murraymcleod wrote:
OK, I found the resistor assembly and removed it for inspection. It looked pretty much like the picture posted by AstroRig except the left coil resistor seemed to be tarnished...

Does the fact that the left coil looked corroded indicate it's necessarily bad?

That does not look like corrosion or tarnishing to me. That looks like thermal damage and I would almost bet that the adjacent thermistor blew and spewed hot gases on the coil giving it that appearance. Does it look like molten metal has leaked out the ends of the thermistor?

Per the Parts Catalog for your motorhome, 2003 SUNOVA ICD27C D-SERIES

The part number for the entire resistor assembly is 103930-01-710 and it is available here: Winnebago Outdoor, Victory 035-0006 RV/Auto Fan Speed Resistor (Fused)

The other alternative is to solder another thermistor inline, leaving the old one in place, as is done at the link below (on a Monaco) but life is too short for that for me.

http://www.irv2.com/forums/f115/dash-a-c-blower-speed-switch-117793.html

[murraymcleod]

[murraymcleod]

Maybe this?