Good Morning All - AND Happy New Year.

Wondering what folks think about this or, if anyone has heard of the phenomenon before.

When I drive with the HVAC Blower fans on, and I apply the brake or use my turn signals, the blower motors pulse with the time of the blinkers and change with the holding of the brake pedal. Crazy thing is the speed of the blowers INCREASE significantly (I say significant - as it is very noticable). This does not happen when the blowers are on and I turn the running or headlights on with the dial knob on the dash. Just blinkers and brake lights.

The overall voltage numbers don't shift down or up. I haven't suffered any ill effects, yet,,,, and I haven't done a LOT to chase this issue down. But I will go on a chase!

I'm looking and asking for "could be's" for anyone with more electrical knowledge to point me in some directions as to cause. One question is,,, can there be damage if left alone? Could it be a symptom of a bad ground? Are they shared circuits at all? I'll be digging into the ED over the next couple of days myself.

 

Yes, a big yes, to the possibility of a bad ground.....as that's a common culprit when really weird things happen.

But where? Which ground?

I'll try to do some checking and mulling later.

Cheers
DD

 

Check out page 678 in Kirby Palm's Book where he describes a similar situation when his turn signals were on, only it affected his cruise control instead. Turned out to be combination of bad fuse panel contacts and a dirty ignition switch. Your problem may be related.

 

Thank you both.

I just have to say,,, I love the electrical diagrams for the XJS. Clean and clear...

That said - look at G12... Yikes.

Im sure I don't understand how a bad ground could cause an issue like this. Is it that with an insufficient ground or a ground that is pushing voltage back into a/the system from another area thru a ground point shared by many grounds can have this effect? As the dude from "vise grip garage" says,,, "I just don't know"!

 

Jay,

Just a thought: as we know corrosion within the Darlington Transistor can cause really weird things including the blowers running at higher speeds or being permanently live and running without the ignition turned on.

I have a problem with mine as my right hand blower runs at Pos II speed even if the blower is set at Pos I speed. And confusingly, that blower also pulses every 4-5 seconds when the blower switch is turned to off.

I'm pretty sure that it will be the Darlington at fault and will get around to investigating it soon.

I wonder if your problem is somehow being caused by a fault in this area?

Good luck

Paul

 

Agggggrh... Thanks Paul.

Not what I was hoping to hear but,,, is what it is. Maybe an XJS right of passage...? Some digging.

I've had one funky moment with the behavior of my blowers that I hauntingly thought might be the Darlington issue. That was months ago and it's never recurred.

I'll start with the "easy" stuff. See what happens.

 

Jay - I was driving the other day and had a similar experience, fan speed changed and was pulsing. Have not driven the car much and after a while things improved.
but not perfect by any stretch.

I also have cold air for a few minutes then the air becomes warm.
Turn off the fan, wait a while and cold air again for a short while..... then warm...also interested in your fix...

 

I hate to say it,,, although I was hoping it was a PAST experience, but I was hoping someone had similar experience with the pulsing... Is your issue in exact time with applying the brake and blinkers and,,, not with running lights and hazards? Just wondering.

The temperatures have really DROPPED in my neck of the woods, and although there are some things I can do working on my machines, things to do with little bits, wiring, plastic and even extended troubleshooting is on hold for a bit. I'll be getting back to this when we get closer to Spring, springing.