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The switches have the original manufacturer's part numbers on them. Trying to find one in "OEM" livery can be pretty tough. Meanwhile, our vendors have sourced the correct switch and you can be sure it's exactly the right one.
For your mechanic and others playing along at home: The switch depends on that copper capillary tube, filled with liquid, to operate a small microswitch. The fluid expands with heat, pushing on a small brass bellows to close the switch. As the fluid cools with AC operation and drops close to freezing, the bellows collapses and the switch opens. The end of the tube passes into the air box through a small hole, and is retained by a small clip with a crew on the outside of the airbox. The copper capillary tube must not be bent with any sharp corners, as it will risk collapsing and blocking fluid flow. Worse, a sharp corner weakens the tube and risks a leak. When it leaks, it fails with the switch in the open position, and no compressor function. So use serious caution when removing or replacing the switch and especially that capillary tube.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Hello
Resurrecting this thread to add reference material:
My evaporator had always been freezing up so I read the freeze switch had an adjustment....then I read there are 2 kinds of freeze switches....one that is adjustable and one that is not...I don't know if I agree with that...the switch in the above pictures has a screw head on the end where the electrical connections go. I have the other one, pictured below. I searched high and low for good pics of this thing and couldn't find any so am providing.
To adjust I went approximately 1/4 turn clockwise then road tested. The air coming out of the vents was absolutely frigid with fan setting of 1 and the temp slider to the coolest setting and running on the highway on 80 degrees or so but with pretty good humidity I could not detect a reduction in air volume coming out of the vents....several times I turned the fan to 4 to see if I could tell that way and it appears that so far the adjustment worked but time will tell...not quite ready to put Jerry's cowl cover back just yet...
The first pic below is the end of my freeze switch with the electrical connections:
This end is facing the drivers' side *LHD - 2 wire connection, standard for both switches....visually if you compare to above posts this end would have the screw head and be a brown plastic or similar type of material.
Pic below is other end of switch...the small phillips head screw you see is the adjuster for this type of switch. Turning it clockwise will raise the temperature that the switch cuts current (which is what I needed in my case; given mine has been freezing) to the compressor. I have the copper tube that goes over the end of the capillary probe so its correct depth-wise (fits over end of capillary probe and tapers outward so you can only push the probe in a certain amount) where it goes into the evaporator chamber.
Small phillips head ....turn clockwise to raise temp. to cut power to the compressor. As a friendly reminder, for those that still have this circuit as a load bearing one; the freeze switch can burn out from current over-draw as the climate board relay...happened to me before I added the relay under the hood to power the compressor and updated pusher fan thankfully this switch is nowhere near the cost or PITA as the climate board relay fix.
With this properly adjusted and the relay under the hood taking load off this circuit and powering the front pusher fan and the A/C trigger wire for the fan controller that runs the 2 main rad fans everything properly cycles with the compressor, courtesy of our correctly adjusted freeze switch on a trigger-level (very low load) circuit.
I hope this info helps as we continue through spring and tackle our seasonal work to get our A/C's optimized for the upcoming warmer weather.
Its not the freeze switch that usually dies - its the relay in the head unit. Taking the load off that relay is still a good idea (contacts are undersized for the load). For model years that have a suppressor relay never remove it from the CE panel unless you want that head unit relay to die (even sooner)...
I’m “optimizing” my AC as well since the refurb last year.
things I’ve learned:
Even with the full R134a conversion treatment, these units can freeze the occupants. Until I got my freeze switch probe set deep enough, my wife and I could (seriously) see our breath freeze. And then after about 45 minutes, air flow would reduce and the cab would start getting warm, since the evap would freeze over.
With the freeze switch probe set in correctly, the cab center vent temp locks in as per the analog thermometer at about 48 degrees. Which still gets uncomfortably cold in the highway, but that is with the recirc flap fixed so as to recirc.
if we want fresh air, I need for the evap to stay cold longer. So, I turned the tuning screw at the freeze switch a quarter turn to (as above) turn off the compressor when the evap coil is even colder a degree and a half or so. And I’ll carefully try and determine if air flow volume is still capable of reaching its max. We’re trying to cheat thermodynamics here. Setting the freeze switch “colder” means the evap will get below freezing and particularly with fresh air, may under conditions still freeze the evap. I may next summer find myself setting the switch back the way it was.
oh, and to REALLY know what’s going on with the evap temp, we (I) should replace that analog vent thermometer with a digital one. And will likely happen.
Just a note to say 'thank you' for the earlier post regarding the re-set for freeze switch cut out temperature. It helped get mine quickly changed from it's 52 degree to 38 degree F 'cut off'. So, cooling with the OE 134a system has been great this hot summer here in PA.
If your recirc circuit is correctly moving things around the time for air-flow testing is when it changes and outside air is passed through the evaporator.
The 134 conversion works very well with these systems and I posted pics on here showing its not difficult to have unrealistic temps coming out of the vents.
Keeping an ice-free condenser gives the system enough time to pull water out so your biological AC runs correctly.
So here is my final take on freeze switch setting tuning.
Before getting the freeze switch probe set in correctly, the vent temp would get to freezing and felt great until the evap froze, air flow was impeded and when parked, a huge puddle would appear after the ice melted.
After finally getting the freeze switch probe set correctly, the compressor cycles on off every 20 seconds or so. The vent temp is 47 degrees and a puddle, albeit much smaller still appears.
there is still some evap freezing. So, further tuning of the freeze switch for colder vent temps doesn’t make sense if I want to choose air flow volume over extremely low vent temp (which would be followed by evap freezing anyway).
10-10-2017, 01:48 AM
1989 S4 A/C Anti Freeze Switch
George Layton March 2014
