jej3

In my continuous exploration of trying to find the optimal AC setup for Florida, I was wondering if there is anything inherently bad about jumpering the Freeze Switch and leaving it that way?

I have just jumpered it and ran the car @ 1500RPMs and saw temperatures of approx 40F at the vent which is the COOLEST I've ever had.

Will I end up with a block of ice if I leave this like this for a while or ?

Thanks for helping the curious

WallyP

If the switch is working properly (it can be tested), jumpering it will have no helpful effect.

If the switch is shutting off the compressor when the evaporator is above freezing, replacing it (or, in some cases, it can be adjusted) will fix the problem and avoid freezing the evaporator.

If the AC refrigeration system is working properly, yes, you should end up with a block of ice in humid weather.

Most 928 HVAC system problems are control problems, faulty heater valves, hot air leakage into the system or into the car, etc.

jej3

Thanks, wally!

If you happen to have a quick link to testing the freeze switch, I'd love to read get it.

WallyP

The freeze switch does not penetrate the refrigerant system. You can carefully pull the probe out and unplug the wires. Check continuity on the switch, put the probe in ice-water, and see if the switch opens within a short time.

A few of the switches have an adjustment screw with a locknut - if so, you can adjust it.

When you put the probe back in the evaporator, make sure that you don't poke a hole in the evaporator, or you will be in a world of hurt. To replace the evaporator, you start by taking the tail-lights out...

jej3

Thank you, Wally. I will consider doing that but at the point I have the switch off, it would seem Freeze switches are easy enough to replace; I may just do that since they appear to be $30-40 from vendors here.

Alan

You still might want to test the new one before you put it in...?

Alan

928 at last

And, just a note, the resulting "Block of Ice" can screw up your evaporator...then you take the tail lights out...and go from there...

The Forgotten On

I started the removal of the evaporator with taking out the seats. Then proceed to remove the entire interior and end up here.


Believe me, you don't want to break it. I did a complete system rebuild because I wanted cold air for the next 15+ years trouble free. You may have to do this if you mess up.

j.kenzie@sbcglobal.net

You can test your freeze switch by pulling it out, putting an ohmeter on the two leads, and putting the probe in a glass of water with a thermometer. Keep adding ice cubes until the switch opens and note the temp. Some are adjustable.
Dave

dr bob

The freeze switch has a capilary tube, and pressure from the expanding fluid inside flexes a brass bellows. The bellows operates a microswitch as it moves, There are inherent long-term problems with using brass in this application, to the point where perhaps the freeze switch could be considered a wearing part of the system.

Here in the dry desert climate of SoCal, I have a freeze switch that's 'frozen' in the closed position. So the compressor runs regardless of evaporator temp. With summertime humidity in the single-digits here, it takes an hour or so for enogh ice to form that the airflow can start getting constricted. Cycle the comprssor off manually, and the ice melts and goes down the evaporator drain. For most driving in town, it isn't on long enogh for freezing to be an issue. If I lived in one of those rare humid areas of Florida, mine would ice up a lot faster I'm sure.

Meanwhile, many "modern" cars use a low-pressure cutoff switch in the suction side of the compressor loop. When suction-side gas pressure drops low enough to risk ice formation in the evaporator, the compressor cycles off for a bit.