Heater fan issues

[fischer5534]

The heater fan on my 2000 SEL occassionally remains running when the ignition is switched off. When this happens pulling the 7.5 amp interior fuse for the relay does not shut it off. Pulling the 40 amp does. Pulling the relay also shuts the fan off.

I've replaced the relay, pulled the relay box out and examined the wiring below the relay all to no effect. Thusfar, the fan seems to shut on its own after a couple of hours.

Any ideas on what may be the problem or further tests? I'm at a loss.

Thanks, Doug

 

[budwich]

Just a small question, do you have an EATC or basic? The two function differently.

 

[fischer5534]

Sorry - Its the basic heat/AC combo.

 

[budwich]

Thanks. As you found, the relay is the key on the basic. Since pulling the 7.5 fuse doesn't "drop" the relay... that's doesn't seem right.... but even then, that fuse only is "stopping" a "hot in run" power connection which I assume is off anyways. Your best bet is a multimeter and do some checks. First look for grounds and power on the "pull up side" of the relay in question. When you said that you replaced it... was it with a new relay or just one from another circuit position? possibly two bad relays... poor odds but who knows.

Oops... another question... which relay do you think you have changed / removed.... the blower relay or the high speed blower relay? both will stop the motor when removed... but the one likely at fault is the blower relay. Both are in the same relay box.

 

[fischer5534]

Thanks for the input, Budwich. The relay I initially replaced (with a new one) was the one in the box beneath the air filter (which I learned about by searching this site.) When I pulled that relay the fan would stop, but replacing it did not solve the problem. I've since checked by owners manual and found that it shows a "fan relay" in the main control box and so I switched it with the one I removed from the auxillary box. The fan has worked fine through a couple of cycles of starting and stopping, but since the problem was sporadic I'm not sure its resolved.

Why would this one fan need two relays? You mentioned a "high Speed" relay, but when the fan would not shut off I could still change its speed to all settings with the rotary switch. Curious, huh?

Doug

 

[budwich]

If you pull the drawing, it is "easy" to see the design. Why are they designed that way... primarily for "reliability".... What happens when the fan is on high, there is alot of current going thru it. Switching that amount of current thru a "normal" rotary switch like that employed on the control panel would mean a large degree of arcing and most likely premature contact failure. So what they do is cause the switch to "activate" a relay. The pull-up winding take less current so the switch doesn't get "hurt". However, the contacts in the relay that form the circuit still "see" that same amount of current. The difference is that you can "easily" pull / replace the relay (ie. serviceable) while replacing the switch would take a "bit more effort". That's my story and I'm sticking to it.... Glad you fixed your problem. My advice about the two relays was slightly off since I only have 96 drawings. The design is basically the same but the location of the two relays is obviously different... in 96 they are in the same box (upfront).

 

[fischer5534]

thanks again for your insights, budwich.

Doug