A/C Temperature Switch.

[86 911 Targa]

For the M/Y 1986 and others, the a/c temperature switch P/N 911-613-121-0 has been superseded by P/N 911-613-121-1.

Are there any hysteresis, and, low temperature cut-off adjustment screws on this part?

Thanks,

Gerry

[kuehl]

What is the issue or objective?

[86 911 Targa]

Hello Kuehl,

And thanks for your help.

1. To reduce the hysteresis time on the compressor from the factory 6f,
to 10f.
This adjustment, eliminated evaporator freeze-up in our high humidity
environment. (see pic#1).

2. Setting the compressor temp cut-off @ 38f(at the center duct) also helps (see pic #2).

Both of these adjustments were available on the original switch.

Thanks,

Gerry

[86 911 Targa]

^^^^^
A/C switch adjustment screws.

[kuehl]

Before you play.

Have you pulled the end of the probe out of the evaporator and
tested the thermostat in a glass of ice?

[86 911 Targa]

Originally Posted by kuehl

Before you play.

Have you pulled the end of the probe out of the evaporator and
tested the thermostat in a glass of ice?

Yes, on the ice test.

Because I could not find the adjustment screws,

I have yet to install the switch.

Thanks,

Gerry

[kuehl]

"To reduce the hysteresis time on the compressor from the factory 6f,
to 10f."

The hysteresis, or on/off time, is 'system' as well as environmentally dependent.
Once the contacts break (system off, clutch off) the dwell time before the contacts make again will be dependent upon the evaporator core temp, air temp moving through the core and volume of air. On a 100F+ day, the dwell time between when you will feel cold air again after the thermostat turns off the compressor could be quite long as compared to a 80F day.

Have you determined at what approximate temperature your new thermostat contacts break when the thermostat is set to max cold (fully CW)?

Normally you don't have to "play" with the thermostat. Most evaporator freezing issues are related to probes contact in the evaporator core.

Verify at what temperature (the ice test) your thermostat opens its contacts when set to max cold.

[Duc Hunter]

I too would like to know if the newer switches have these adjustment screws. My new system can produce vent temps in the 20's on an 85 degree day if I want.....and while nice the system obviously freezes quick. If I could set the cut off so it was at 36-38 even core temp this way...it would be a life saver.

I agree with Kuel, it would be systems/car dependent.....and it would be easy to do. Have the passenger floor board out and a passenger with a remote thermostat....also have the temp switch out.....drive the car with they system on full cold, and adjust the screw so the compressor shuts off when the core gets down to the desired temp (36-38 in my case). Go home and button it all up. Sounds easy enough (in my head )

I did not check mine before install.

[86 911 Targa]

Originally Posted by Duc Hunter

I too would like to know if the newer switches have these adjustment screws. My new system can produce vent temps in the 20's on an 85 degree day if I want.....and while nice the system obviously freezes quick. If I could set the cut off so it was at 36-38 even core temp this way...it would be a life saver.

I agree with Kuel, it would be systems/car dependent.....and it would be easy to do. Have the passenger floor board out and a passenger with a remote thermostat....also have the temp switch out.....drive the car with they system on full cold, and adjust the screw so the compressor shuts off when the core gets down to the desired temp (36-38 in my case). Go home and button it all up. Sounds easy enough (in my head )

I did not check mine before install.

This is exactly what I did with the original factory switch.


^^^^^
With the temp & fan switches in these positions.


^^^^^
This was the center duct temp on an 80f day.

The hysteresis on the compressor was:

1. On at 52f.

2. Off at 40f.

I don't think it wise to exceed 38f at the center duct,
as the evaporator might be @32f.

By rotating the temp control to max, I was, like you posted
able to reach temps of 25f at the center duct.

So back to my original question, are there adjustment screws
on the new (updated) switch.

Thanks,

Gerry

[86 911 Targa]

Originally Posted by kuehl

"To reduce the hysteresis time on the compressor from the factory 6f,
to 10f."

The hysteresis, or on/off time, is 'system' as well as environmentally dependent.
Once the contacts break (system off, clutch off) the dwell time before the contacts make again will be dependent upon the evaporator core temp, air temp moving through the core and volume of air. On a 100F+ day, the dwell time between when you will feel cold air again after the thermostat turns off the compressor could be quite long as compared to a 80F day.

Have you determined at what approximate temperature your new thermostat contacts break when the thermostat is set to max cold (fully CW)?

Normally you don't have to "play" with the thermostat. Most evaporator freezing issues are related to probes contact in the evaporator core.

Verify at what temperature (the ice test) your thermostat opens its contacts when set to max cold.

The defective switch is out of the car, so, I'm unable the determine the thermostat
operating parameters.

So, does anyone know if there are any adjustments on the new replacement switch?

Gerry

[86 911 Targa]

Don't want to play "Fingerpoken"...........

[ganun]

That's why I went with a digital controller, can tune the hysteresis accurately, and on the fly from the cabin. Only thing is dunno how reliable over time.
See my old thread.