tomshark

here are my symptons
85 euro.
interior fan works / control unit works as far as vent control and heat..

electric fan does not come on
a/c light on a/c button does not turn on when engaged.
never gets cold.
freon is full no leak.
i hear no noise of the clutch engaging on compressor .
nothing is frosted over or even feels cold ....

thanks for any ideas were to start

AO

This is the best overall writeup.

https://www.928gt.com/t-wallyhvac.aspx

SharkSkin

Start here: https://www.928gt.com/T-WallyHVAC.aspx (I see Andrew beat me to it)

Chris Hansen

That is one nice write-up!

911tracker85

thanks for this link. one of several issues on my 'to do' list for my 84 I bought last fall. unfortunately I have not completed enough of the maintenance to be comfortable driving it to SITM. and now my 911 is way too track oriented to drive that far.

building up a list of stuff to order from Roger. list just got longer earlier today seeing the heater control valve / hose posting. and so it goes, but loving my shark.

hopefully next year.

Jfrahm

Since the relay in the HVAC head is undersized for the AC compressor clutch and can burn out, I fitted a foglight style relay and powered my AC clutch through the relay, power from the jump terminal block (with an inline fuse, of course.) It was a pretty easy job. Now my HVAC head relay only powers the new relay and won't burn out. These relays can be found in the auto parts store, some with a handy mounting tab.

-Joel.

dr bob

Tom--

Per Wally's excellent write-up, start with some of the easy stuff, particularly the fuses.


I had the radio out one time, and managed to dislodge the little connector that's on the back of the AC button on that little separate panel. The little multi-pin connector there has no retainer, so a tug on the wiring was all it took to pull it off. Once disconnected, you'll get the symptoms you describe: No AC button light when pressed, so cooling fan start on button press, etc. Oh, and no cooling. It's possible to access the subject connector by removing the driver's side carpet panel on the console. Or you can carefully pry out the H-shaped plastic trim around the vents, and the HVAC and AC button panels, unscrew the little retaining screws for the AC button panel, and reseat the errant connector.

HTH!

SharkSkin

On the subject of the relay inside the AC control head -- 78/79 cars don't have that relay, they just have a simple contact. Nevertheless, I installed a power relay to protect those contacts and the hard-to-find speed relay.

For info on one approach -- grafting the power relay into an unused socket in the CE panel -- see this page. Yours will be wired differently but IMHO this general approach can be made to work in any 928.

tomshark

thanks for info and yes i removed stereo .
i just jumped relay xviii and then the aux fan worked .
replaced relay with known good still nothing . i would say dr. bob may be the winner .

tomshark

after further looking and the control units out i have noticed 3 things
one wire connecter was not attached and 1 black wire had become detached from solder in back of info panel
and the bulb for the ac button is dead . it is marked 16 v????
auxilary fan is still not coming on

WallyP

On the pre-S4 cars, the aux cooling fan is triggered by refrigerant temperature, not pressure as on the later cars. This is much less efficient in triggering. That is one of the major reasons for installing an additional relay in the system. An additional relay, triggered by the A/C compressor signal from the small head relay, can be wired to operate both the compressor clutch (relieving load on the small head relay) and the aux fan (ensuring that it is running all the time that the compressor is operating).

tomshark

i am getting a little lost .
i should attach new relay from line out ( WHEN AC SWITCH IS ACTIVATED) directly to the
ac clutch and aux fan wiring ?
also if i jump relay xviii i got aux fan to run would this also make as clutch to come on?
i am sorry for all the questions but i am really confused and i do not want to wire anything wrong .
also the bulb in the ac switc is dead what is the right part number . it is marked 16v

dr bob

Tom--

Start out by restoring the basic functionality. Generally, the little panel is serviceable. but if there are broken wires/connections and a dead bulb, youmay be better off getting a good used one so it's a plug-and-cold solution. Maybe your soldering skils are graet and you want to hunt for the bulb and install it, that's fine. 928 International and our other used parts sponsors have these available, and I'll speculate that they aren't real expensive.

Once all that stuff is working again, --THEN-- consider following Dave and Wally's advice about adding an external AC clutch relay. The little relay in the AC control head manages the AC compressor clutch operation, and is undersized for the duty. There are a couple options for beefing up the capacity. One option is to wire a relay to replace the one that's in there now. Second option is to add a new relay at the front of the car, triggered by the existing relay. Again, depending on your soldering skills and such, you may decide that a hidden relay at the control head is a better option for you. If you are more of a crimp connector type of electrical yech, the relay at the front apron might be better for you. Wally's AC diagnosis covers the trouibleshooting steps that will help you determine if that's part of your problem. Symptoms you describe took me to the little button panel first, though.

SharkSkin

Always good advice with these cars. First, make it work as designed. Then you have a solid basis for any upgrades.

tomshark

once again on this car cleaning the connections works wonders. i now have a/c cost emery cloth.
in the fornt coming off evap unit four way connetor , also cleaned a/c switch which also was turning green .
thanks everyone