I have a 1987 300 TD wagon. The air conditioning was upgraded a few years ago from R12 to one of the supposedly-more-environmentally friendly refrigerants (134a I guess). The air conditioning is acting up, and I would really appreciate some thoughts as to possible causes and remedies.

Here are the symptoms:

1. When the AC works, it works well. Blows nice and cold. However, it does not always work.

2. If I set the temperature control to "min" and push the low fan button, the AC seems to work fine on low.

3. If I set the temperature control to "min" (or any other cold setting) and push the auto button, the AC works fine for a little while; but, it stops cooling after 5 or 10 mins. If I turn the ignition off and back on, it resets and works fine for 5 or 10 min again, then stops cooling. I can keep resetting the ignition every 5 or 10 min, but that gets old pretty quick and may be dangerous to do while driving. Sometimes on longer trips, after resetting the ignition several times, the AC will continue working for the duration of the trip -- but that is rare.

The fact that resetting the ignition makes the AC work for a while leads me to believe that a relay or some other electrical component is bad. Any ideas?