A/C Diagnose - Temp switch vs Fan switch

[B.Green]

Searched a lot but need a referee call - Sorry for basic question. 88 Carrera

My A/C compressor clutch engages as soon as Fan switch is rotated CW to first detent even with A/C Temperature switch fully CCW (rotated left)

My mechanic felt that compressor clutch should not come on if Temp switch is fully CCW - therefore leaving me free to use Fan switch for airflow without A/C. So I was headed towards troubleshooting Temp switch based on what I understood to be a few posts indicating that operation had been restored after cleaning contacts.

Preparing for the work with Bently manual, it describes the function of the system as:
Temp Control Knob - fully left for low cooling - fully right for full cooling.

Fan Switch - Position 1 no cooling / blower off. Positions 2 to 4 A/C on, increasing blower.

This leads me to believe my system is working as designed - except that it might be be working the A/C compressor/system too hard at lowest Temp setting.

So does this mean that A/C blower fan CANNOT be used for cockpit ventilation/cooling WITHOUT A/C compressor working?

I would like to get air from center/side registers without always having to use A/C.

Thank you for your confirmation.

[GH85Carrera]

On my 85 the compressor always kicks on as soon as the fan is turned on. If the temp switch is all the way down the temp will cool the sensor in the evaporator fairly quickly. The compressor will start to cycle fairly soon. It will still cycle on and off occasionally no matter what the outside temp.

[Barrpete]

The temperature switch only functions to turn the compressor on/off based on the temperature it senses in the evaporator. So unless the ambient temperature is pretty low, even at the lowest setting on the temp switch the compressor should kick on.

Also, the system does not bring any outside air into the cabin. Its a closed loop. Air flows from the cabin through the opening under the passenger floorboard, then through the evaporator and back into the cabin. So the AC blower fan can't be used for ventilation or cooling even without the compressor working.

[86 911 Targa]

Originally Posted by B.Green

Searched a lot but need a referee call - Sorry for basic question. 88 Carrera

My A/C compressor clutch engages as soon as Fan switch is rotated CW to first detent even with A/C Temperature switch fully CCW (rotated left)

My mechanic felt that compressor clutch should not come on if Temp switch is fully CCW - therefore leaving me free to use Fan switch for airflow without A/C. So I was headed towards troubleshooting Temp switch based on what I understood to be a few posts indicating that operation had been restored after cleaning contacts.

Preparing for the work with Bently manual, it describes the function of the system as:
Temp Control Knob - fully left for low cooling - fully right for full cooling.

Fan Switch - Position 1 no cooling / blower off. Positions 2 to 4 A/C on, increasing blower.

This leads me to believe my system is working as designed - except that it might be be working the A/C compressor/system too hard at lowest Temp setting.

So does this mean that A/C blower fan CANNOT be used for cockpit ventilation/cooling WITHOUT A/C compressor working?

I would like to get air from center/side registers without always having to use A/C.

Thank you for your confirmation.

Your system seems to be operating as intended.

As per the previous post, compressor activation is dependent on temp switch position, and the signal from the evaporator throught the capillary tube to the temp switch.

For minimum compressor "on" time, the temp switch should be fully CCW, and the fan on position 4.

You could re-wire the two green wires in back of the temp switch to activate the compressor per your requirement.

Good luck,

Gerry

[B.Green]

Thanks to all AGAIN. What a great host and members.

You saved me from trying to "fix" something that wouldn't change. Now to review posts regarding the A/C Temp switch capilary tube to see if it might be causing the compressor to stay on all of the time. I sense mine is staying on all of the time.

[86 911 Targa]

Originally Posted by B.Green

Thanks to all AGAIN. What a great host and members.

You saved me from trying to "fix" something that wouldn't change. Now to review posts regarding the A/C Temp switch capilary tube to see if it might be causing the compressor to stay on all of the time. I sense mine is staying on all of the time.

Check the position of the capillary tube on the evaporator.

Also, you might want to clean the switch contacts.

If you remove the temp switch, be VERY CAREFUL of the capilary tube.

pm me as needed.