Fuses Cleaned.,.. Small problem

[jeffmc]

I just used some advice on a prior post..My 85 5 speed 928(American).. I was having a problem with my interior lights and radio not working. I pulled all the fuses(Not the relays-weather got bad)and sprayed the fuse box with a electric contact cleaner. I let the fuse box dry and replaced all the fuses. Problem solved with the radio and interior lights. They work now.. Everything seems to work fine except now the fresh air blower stays on. You can adjust it's speed but when it is on "0" it is still running(very low).. Before it would cut on and off normal. I pulled the 30 amp fuse and blower relay and it works as if they are still in.. Any advice? I have heard of the "Magic Blower Syndrome".. Is this it?.... Thanks again for any tips.. Jeff

[Maleficio]

It runs constantly.

[Landseer]

all the time...when the lower slider on the HVAC system is not full-off.

[jeffmc]

Originally Posted by Maleficio

It runs constantly.

Yes... When the switch is on "0" it is still runs very slow.. I pulled the #5 relay and the fresh air blower 30 amp fuses for the fresh air blower and it still will works on "0"...

[Landseer]

If you pulled the #5 relay your turn signals won't work.
Which fuse was pulled? Should be 17.

Try pulling roman numeral X and see what that does.
If still running, pull VIII.

Magic blower is cycling between full-on and off; so far this isn't happening for this car.

[jeffmc]

Originally Posted by Landseer

If you pulled the #5 relay your turn signals won't work.
Which fuse was pulled? Should be 17.

Try pulling roman numeral X and see what that does.
If still running, pull VIII.

Magic blower is cycling between full-on and off; so far this isn't happening for this car.

I pulled the #5 relay and #17 fuse.. It still blows on "0".. I will try the X and VIII and let you know what happens... Thanks

[jeffmc]

I pulled the blower fuse. The blower relay and the X and VIII relays at the sametime.. The blower still runs.... STRANGE?

[Landseer]

Yes. Major wiring problems.
Did you pull the panel out on this car yet?
That's the best place to start I think.
Check the back for melted wires causing the cross circuit.

One relay provides power for normal operation. Fan operates by default at low speed if knob is at zero, if bottom HVAC slider is not full left. Otherwise, knob has no function until slider is pushed away from left "off" position.

The other relay provides full power only -- when bottom slider is at defrost, regardless of knob position.

Only a short will cause the blower fan to run if these relays are missing.

There is a big coil resistor in the air plenum that can fail in a couple ways. The slow fan speed is created by engaging more coils to divert the electricity into heat. It can get into a weird cycling mode, causing full off/ full on interations. Thats magic blower.



There is a tiny, silent fan in dash always running behind that little round grate on the console, thats for air temp sampling. I think its unfused, unrelayed, but you never hear it running.

[riber.bentsen]

I can hear mine running (little air temp sensor in dash) ONLY when the slider is full left on "0". Don't you think that may be what you are hearing?

[jeffmc]

Thanks for the info guys... Today it quit running for sure(HVAC).. It has been making a growlng noise for a little while now and it quit running today. I will take a part this weekend and give a look..

[Landseer]

The way to campaign through that problem is pull panel, then mark and pull hood. Then, remove fan and drill a tiny lube hole. That will give it some new life. Then reinstall. Then clean CE panel, replace all the 53 style relays and fuses and look deep within the wires for shorts. Should solve it all and give you the opportunity to clean the air plenum, seal the fan to prevent leaks and get a good look at other wiring issues if they exist. Great basic starting place to build the foundation.