Air conditioning help? 1986 190e

Now that I have a perfect working sun roof(thanks gang), my next issue is the AC...
Yesterday was a hot day here in Seattle, but the AC seemed to work ok.
This was kind of amazing since the AC never worked since I bought the car two months or so ago...
Today, nothing.
I have read through some of the posts here and it kind of looks like there are at least two issues which "might" cause intermittent AC issues.
1) Low pressure switch on AC condenser. This seems kind of unlikely to me, since one would think the AC would consistently work to point.
2) Speed difference senser on compressor to prevent seized compressor from killing serpentine belt.
Any other thought on what could cause this kind of intermittent issue? Relays?
Thanks for any or all thoughts. Marty
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I wouldn't suspect either two... first of all, measure the low side pressure... If you still have R-12, the pressure should be around 37 PSI when compressor is running... R134, the pressure should be around 34 PSI.
Car windows and doors must be closed when you measure and you must wait after 5 minutes of running the A/C on max.
If the compressor is not running, the pressure should be around 120 PSI.. roughly.
Do this first and then we'll go from here... The place to measure is above your driver side front wheel location. It is pretty close to the shock tower.
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