A/C temperature switch

geoz · 07-21-2009, 06:18 PM

i guess I'm not the first with the problem (I believe my temperature switch may be shot) but I can't believe the solution is still to install a piece of kit that relies on a thin gas filled pipe triggering a mechanical switch. this may have been cutting edge 20 years ago, but I can't believe there is no simple & less vulnerable solution to this.

Has anyone come up with a simple little design based on a temp resistor or similar? all the thing needs to do is switch the compressor on & off, right? why can't that be triggered via a little pcb, with a temp sensing resistor attached to the evaporator, and another reference point set through a poti connected to the knob on the console?

has anyone done this or knows of a solution? that would be much appreciated.

86 911 Targa · 07-22-2009, 06:38 AM

Georgie,

Buy a new temp switch and a six pack of Crown Lager.

That will fix everything.

Cheers,

Gerry

Mitch Leland · Mitch Leland's Garage

Quote:

Originally Posted by 86 911 Targa

Georgie,

Buy a new temp switch and a six pack of Crown Lager.

That will fix everything.

Cheers,

Gerry

Gerry,

So why doesn't Georgie's hypothesis work?

Thanks,

geoz · 07-22-2009, 10:35 AM

Gerry,

cool approach (on more than one level).
I'm just looking at why the tube breaks and it seems almost inevitable given the tight space. An electronic setup would just be much less vulnerable. Cheaper too.

86 911 Targa · 04:14 PM

Geoz,

One of the issues with the "tube" is the material.

Being constructed out of aluminum, it is very fragile to bending,
which is the reason for the brass tube (guide) which is inserted
in the evaporator.

Also, the tube has a long run from the switch to the evaporator.

As for an electronic type sensor, many of the auto manufacturers
have kept the tube sensor for many years, perhaps as a cost
effective/accurate approach.

You may wish to enquire with the dealer if another approach is
currently used on recent 911's.

When (if) you replace your sensor, take great care in placing it
through the body.

Maybe a friend can help guide it into the front of the car.

To prevent any vibration, be sure to secure the tube to the fan housing
with some sturdy tape. (I use Gorilla Tape).

Email me if you want pics.

Also, kuehl posted an exemplary tutorial on A/C.

Everybody should read it!

Good luck,

Gerry

DDD · 08-01-2009, 11:13 AM

Geoz: I had a similar post about two years ago. You can search on it by my ID - DDD. I totally agree. Switch does two things. First, it allows you to increase the temp in the cabin by setting it so that the clutch will cycle on and off (and, as I understand it, allows you to totally keep the compressor off and just get fresh air at the far counter clockwise setting). This is stupid -- no one would ever think the a/c is blowing TOO much cold air in these cars. Second, it prevents the evaporator (I think) from icing up by cycling the compressor. I think this is also pretty unlikely (mine has never cycled), but even so, why not just a simple wire with a temp sensor, rather than this delicate little tube? I don't think icing causes damage -- just restricts airflow. Why so much concern over this that Porsche had to put this tube in place? I don'tget it.

I ended up just bypassing my switch with a jumper behind the console. I still think it would be good to find a different on/off switch that would eliminate the tube, but not sure what would work. --DDD

JFairman · 08-01-2009, 01:57 PM

The design of the temp switch is so simple and it works perfectly till the points burn up or rough handling damages the capillary tube.

I've never seen the little dime sized internal aluminum bellows that opens and closes the points go bad or the linkage between it and the contact points fail.
The points are switching the condensor clutch on and off though and unless you install a relay in the circuit to lower the current going through the temp switch, the points will eventually burn up.

It's a perfect example of kiss... there is VERY little to go wrong with the mechanical temp switch while the alternative electronic setup thats been suggested has lots of difficult to diagnose things that can go wrong and will go wrong while drawing more current from the very expensive little alternator in these cars.

geoz · 08-02-2009, 01:15 AM

not sure how a few resistors and a transistor or two could be less reliable than a gas filled capillary tube.
i might look into this going forward, first i need to figure out if the tube is bad at all.

Giantman · 08-02-2009, 03:21 AM

Keep us posted on your progress ya?

DDD · 08-02-2009, 03:35 AM

I see a temp switch on the Pelican site for only $40 (I thought I read somewhere that it was no longer available). I might just buy it at that price and give it a try (though I can't tell if it includes the capillary -- I assume it must).

I still wish the switch was binary, even if the ice-over protection is needed as a cutoff for the compressor. Just turn on the compressor, or turn it off. And, I wish you could run the fan without the a/c (which I guess you can by turning existing switch all the way down - never tried that).