Crisis

For the last while, I noticed my HVAC blower would only run on "4". This was after a period of intermittent operation at the lower speeds. Doing a Rennlist search, it appeared to be typical "magic blower" syndrome. So, today, I bit the bullet and pulled the resistor pack. After a thorough cleaning, I reinstalled it and was immediately disappointed to see that it made no difference. Then I tried it again and the fan would actually run on all speeds. I figured that I should still be ordering a new resistor pack, but at least it was working in the short term.

My pleasure was short-lived, however, as I soon came to realize that regardless of where I had the controls set, it was only blowing out of the defrost vents at the base of the windshield. Searching past posts has revealed some info on temperature mixing, but I couldn't find anything on my issue. Then, just to top things off, the fan started working only on "4" again. So, I'm back to having either full blast through the defrost vent or nothing. At least the temperature control works and my resistor pack is on order.

Any advice for the mechanically limited would be much appreciated.

the flyin' scotsman

Laird......HVAC direction is controlled through the HVAC head sending electrical signals to solenoids which open/close vacuum source. The vacuum is sent though hard lines to diaphrams in the floor, console, defrost, recirc flap, heater valve which all do fail but unusual to all fail at once.

Rather than repeat whats already written Walleys write up on the HVAC system explains all and Dwaynes HVAC tshoot and R&R is pictoral excellence:

http://www.928gt.com/Default1.htm

http://dwaynesgarage.norcal928.org/1...0Procedure.htm

Crisis

Thanks Malcolm. I'd taken a quick scan of Wally's write-up and was discouraged by the focus on the vacuum system (with which I have zero experience). Dwayne's step-by-step procedure with pictures is both incredibly detailed and intimidating. But learning is a life-long experience, so it looks like I'll get a vacumm tester and dig into it. I'll drop you a PM if I'm headed out your way this summer.

the flyin' scotsman

Also look at John Pirtles site......you should be looking to diagnose whether the issue is electrical (HVAC head) or vacuum.

The first thing I'd check are the associated fuses and relays.

Remember, when the vacuum/ diaphrams fail there default position is open or closed......defrost is open for sure.

Crisis

Well, I checked everything that I could think of in the relay/fuse department. Other than the Defrost relay, do you think it could be any other relay? Likewise, I checked the fuses for cooling flap, blower, control unit, air conditioning - basically anything that remotely sounded like it might have anything to do with the HVAC. All were good, of course. Any other non-vacuum ideas?

Just to keep things interesting, my schitzophrenic blower fan is working on all speeds again today.

the flyin' scotsman

have you been in behind the centre console......radio? anything?

just thinkin that one of the 2 connectors to the HVAC head is loose?

Crisis

Haven't opened up anything there yet. That'll probably have to wait until a weekend, and I'll go down the vacuum route if I can't find anything loose back there. Thanks for the continued help.

the flyin' scotsman

no worries......did it happen over time or sudden?

Crisis

Unfortunately it's kind of tough to tell. I drove the car sparingly last year and my HVAC focus was more on the "all or nothing" fan speed issue more than the "where is it blowing from" issue. I first noticed it when working on the blower fan issue this past weekend, but I think it may have been like that last year as well. I do believe it to be sudden rather than gradual/intermittent, but couldn't swear to it.

the flyin' scotsman

as mentioned the vacuum diaphrams do fail but highly unlikely all at once.

given that the issue was sudden I'd be inclined to believe its electrical and perhaps the head unit itself. If you read Dwaynes write he describes how to remove the head without taking the entire console apart then the wiring can be inspected and head unit manipulated.