johnfm

Charged battery last night as it was starting to crank a bit slow - this cars starts great, runs great BUT no heater blower????

WTF!

The CCU seems to be working in that I get cold air on th eblue dot or hot air on the red dot, but without the blowers working there is no usable heating.

Checked fuse #1, its OK. Adrian's book is at home hence the post.

What to check next....

Jim Howley

John,

I have just replaced my rear blower fan so am aware of what a pain it is not having the fans.

Check the resistor for the rear blower circuit if the fuse is ok.

Otherwise it's possible the motor itself has gone. Mine had and when I took it out it was black and burned.

HTH

Jim.

johnfm

Rear blower WAS fine this morning when I checked it - my problem is no front blowers. Does the front blower operation depend on the rear blower?

Failin gthat, maybe I disturbed some wiring in the front compartment while cahrging the battery??

Adrian

Dear John,
Yes the front blowers are dependant upon the rear blower. I would be checking the rear blower fuse.
Remember you have 2 front blowers, left and right. Left for the left side and right for the right side. What happens when you hit defrost?
I am afraid it is back to basics starting at the rear. From your post I genuinely suspect a rear blower problem.
Ciao,
Adrian
964C4

johnfm

Adrian

thanks for reply - as I posted, your book is at home & I am at the office.

When I got to work this morning I checked the rear blower when I stopped the car - it WAS working when I jiggled the temp sensor ( the one that sticks into the ducting ). The fan worked. I checked the fuses too - OK.

When I rechecked about 15 minutes ago, the rear fan did not work with ignition on and temp dial set to the red dot, nor with disconnecting the temp sensor (which 'should' set it the fan on I think).

Anyway, I'll recheck the rear stuff - it justs seems coincidental that it fails the morning after I recharge the battery.

I take it I can 'jumper' the rear blower relay to check fan operation, much the same way as the oil cooler??

Randall G.

>I take it I can 'jumper' the rear blower relay to check fan operation, much the same way as the oil cooler??

Yes, this is true, if you can find the little numbers on the plug. You can also check #2, #3 & #8 for 12V power.

Good luck!

johnfm

I knew I'd hear from you Randall when the states woke up!! Good to hear from you.

I'm trying to figure out how charging the battery could have damaged anything??

Adrian

Dear John,
Did you remove the battery to charge it?
Did not charge it with battery in place but with negative lead disconnected?
or
did you charge it with battery connected?
The later is not recommended unless using trickle charge.
The type of battery charger you use also plays a role. The swiching or cycling type must have the battery disconnected.
Ciao,
Adrian
964C4

Randall G.

Hey John,

I'm guessing it's just a coincidence that your interior fans started acting up after charging. Unless you did something really strange (uh, stupid ), and I doubt that's the case.

Are you pretty sure neither front blower is operating (based on what you can hear/feel)? Or, is it possible only one blower is out (based on feel/lack of air at one vent)? I mention this in case you have a non-common mode problem with the CCU or final stage regulator for either the left or right-front (interior) fans . As you know, the fuse and rear blower are common to both interior fans.

With regard to disconnecting the temperature sensor and the rear blower running. Several 993 owners, and myself, have demonstrated that the rear blower will fire up in slow-speed if the sensor is disconnected, ignition off, engine cold. Then again, this is not precisely repeatable. On at least one occasion, nothing has happened after disconnecting the temperature sensor on my own car, until after I've cycled the ignition on and off...or some sequence that I can't recall and wasn't intuitive. I haven't taken the time to perform testing to figure out why it works most of the time, but not all of the time.

I think Adrian has you going in the right direction, re-checking the rear blower.

johnfm

I am officially STUPID!! - BUT I have unearthed an interesting - though useless, fact.

The story

My battery charger had blown a fuse, so in desperate need of a 15A fuse, I borrowed fuse 28- Control unit, rear window defogger, outside mirror adjustment, rear wiper.

BUT, when I replaced it I accidently put it in EMPTY slot 26. I realised this tonight when rear demister didn't work.

Relaced fuse into slot 28 and all is working again!

SO, strangely, this fuse also has some connection to the HVAC system - that's one for your 2nd edition Adrian!!


Yours sincerely

Mr Stupid!

Adrian

Dear John,
Not necessarily fuse 28 but slot 26. Wonder what you hooked up by inserting a fuse into it?
Ciao,
Adrian
964C4

robmug

LOL!

At least it's fixed...I wish the failed alternator on my BMW was this simple...

Randall G.

Stupid, but warm.

LOL!

Randall G.

Adrian....I looked at slot #26 in the shop manual, it's not used. On the other hand, fuse #28 supplies "term X" on the CCU. Which would be the likely source of John's problem, wouldn't you agree?

Now, if we're so smart, why didn't any of us suggest to John that he check to see if he had removed fuse #28, and used it in his battery charger?

Adrian

Dear Randall,
Seeing as fuse 28 supplies power to the ccu for some reason then its removal would interfere or shut down some functions within the ccu. I have not looked myself, I believe you. Obviously it did not shut down all functions. Which does not surprise me because the fresh air system must remain active by law.
This is a bit like the 12V supplied to the seat heating also being used for the PDAS/ABS control unit on the C4. Short this out and you fry the control unit.
I have no idea why none of us thought of this before. Just goes to show that there is more to learn.
Ciao,
Adrian
964C4