Don Carter

Sorry, didn't scroll to the right all the way.

I know the relay has an upside down 53 on it just like the ones around it, but I can check the part#.

6, 2, & 8 are tied together.

Alan

Don it does appear that the input from the blower switch for full speed isn't working - these are the black wires - if speed 4 this must be battery voltage. Seems it is not in your results - even without the resistor pack.

The results with the resistor pack don't make sense either - the voltage on pin 8 should be higher as the speed is increased on the switch - obviously it is not....

Check the switch first...

Alan

Don Carter

Well, the voltage does increase on pin 8 when fan speed is increased, but it never goes above 5v.

Agree the speed 4 voltage is just missing. Maybe fixing that would somehow resolve the issue with the othe speeds. I guess pulling the switch is next. I happen to have a spare I could try if it's removable from the head unit.

Never pulled the control unit before, so should be fun. Maybe I'll get lucky and it won't hit 100 tomorrow :-)

dr bob

Don--

Connector for the swith is on the driver's side of the controller close to the faceplate. You may be able to pullthe carpeted cover off the side of the console and push the connector on tight to the controller without removing it or disturbing the other wiring to it.

Don Carter

Thanks!, great idea, I'll try that first.

On the spare control unit I have, I'm not seeing how the switch can be replaced. I was able to get the guts of the switch to slide about a 1/4" out towards the side but that's about it. Maybe the **** prys off?

... Just downloaded and read a PDF you created in 1998 about the external relay mod. I'm suspicious of my relay as well since I have some other weird stuff going on, compressor cycling and stuff like that, but that's for another thread.

dr bob

Don, if you know which control head you'll use, do the relay mod now and get it out of the way. Many folks have been using a commonly-available Radio Shack relay for that fix, and the pins are a little different from what I used and documented. I may still have that CAD file someplace (that was over ten years ago...) and may update the drawing with the R-S relay info.

dr bob

Also--

I don't think you can change the blower switch separately. It has a fiber optic cable running through the to the button for illumionation too, so use caution. Prying the button off will damage that fiber for sure.

Alan

Err I don't think so - the speed number is illuminated not the ****... (check it?). Some have done an aftermarket mod for this as it seems the **** was originally designed for illumination.

The **** just pulls off - be warned its tight but thats how it comes off.

Alan

Don Carter

I couldn't get to the fan switch plug by removing the side panel so proceeded to remove the control unit. Amazing how easy it is to get it out.... except for the fan switch plug. It's really stuck on. Could be some serious corrosion holding it on. I'm prying and twisting with a flat head screwdriver, but all it's doing is chewing up the plastic. There are no clips I can see holding it on, so I guess I just need to force it.

Don Carter

WhooHoo! With some serious force, I got it off and found a problem. The reason it was so hard to get off wasn't corrosion but plastic fused together. The melted plug is terminal five which feeds full voltage to the switch. I was expecting there to be an issue with terminal 4 since that's the one that feeds full power to the blower on speed 4, which I don't have. It looks like I should be able to trim away the melted plastic and clean up the contacts, and test.

Also time to open up the control unit and take a look at the relays.

Don Carter

FAN SPEED IS FIXED!!!!

Cleaned the terminal and hooked it up for a quick test. It's working perfectly on all speeds.

Thanks all for the help and guidance. Still have other AC issues to fix, but this was a big one.

The inside of the control unit is spotless, like brand new. I popped the cover off the relay and it is also like new, no signs of any buildup on the contacts or arching, so I think for now I'll skip the relay upgrade, knowing that it's easy to get the unit out again later if needed.

dr bob

Great news! I love a story with a happy ending!

Alan

Good! glad it worked out

Sometimes its obvious... and sometimes you just have to keep turning over the rocks until you find the culprit... a few rocks on this one...

Alan

dr bob

Looking at the 'problem' again, that's really a 'symptom' of some resistance in the connection generating a bit of heat. Be Sure to improve the connection on that pin so you don't melt the plastic again/more.

Alan-

Looked in my demo controller anad, as always, you are correct on the fiber routing-- it runs to the little window with the speed number. This controller is a star candidate for LED illumination instead of the fibers. I'm sure that the fiber was a bleeding-edge solution at the time the controller was designed. It's way trailing-edge technology now.

Don Carter

Right, something caused all the heat to build up. The blower speed problem first occurred when it was in a shop 5 or 6 years ago having AC work done.

Turned out I had the perfect tool for cleaning the female plug. A Dremel bit that's like a little straight rod, about 1/8" in diameter, coated with diamond dust or whatever. A strip of 220 sand paper did a good job on the male pins.

The car is now back at the shop that installed the compressor so they can look again for the HUGE freon leak. (it had foam in the sight glass the next day after they charged it) They had it for nearly 2 weeks looking for the fan speed issue, and I finally gave up on them, so it was a lot of fun to announce that it was fixed :-)