Open Road

My 88 S4 has been recently topped off with R12. The A/C blows cold but after about 30 minutes it starts to warm up a bit. I have replaced the water valve and it did not make any difference. Does everyone think the freeze switch is the next likely suspect? Just wondering if there was something else to check before ordering a new one.

Thanks

Freeze switch. Stick it in salty ice water with a thermometer and an Ohmmeter between the pins and see if the circuit goes open ‘round freezing.

New ones need to be calibrated/checked. There’s an adjustment screw.

Caveat: a busted freeze switch causes the evaporator to become coated with ice. The result is very decreased airflow through the heater box and warmer air.

If you do not have a noticeable decrease in air volume then it may not be the freeze switch.

Come to think of it, the amount of airflow through the vents does seem to be less. Thanks for the reply. I will get one on order from Rog.

If you shut the AC off, but let the fan continue to run, in a few minutes, air volume should increase - if the freeze switch is not functioning correctly (ice on evaporator will melt, allowing air flow). Just a test to verify that evaporator freeze up is the problem.