I concur with Larry. Ninety degrees isn't too big a problem if you are driving. Anything over 40MPH for five minutes ought to do it.

All the old diesels I've owned or driven had marginal a/c in stop-and-go conditions. It takes a long time for a heat soaked 123 to get comfortable if you start it up and just let it idle. I think there are a couple of issues at play. For one, the compressor just doesn't do enough "compressing" at low engine speeds, and the very low idle speed of the diesels exacerbates this problem. You can see this on your guages - the low side is about 40PSI at idle, right? Drops to 25 when you rev the engine to 1500 RPMs. Evaporator temperature corresponds directly to low side pressure, so the evap is warmer at idle than when driving. The older cars don't have great condensers or condenser fan systems either, so they can't reject all that much heat at idle.

Are you aware the 123 cars use 20% fresh air even when in recirculate mode? One of the standard Texas hacks is to modify the system to use 100% recirculated air. On really hot, humid days this will get you about 5 degrees cooler discharge air.

A good window tint helps a lot! Good tint reflects a high percentage of the infrared spectrum, which reduces heat gain. It helps the car cool down faster when you do switch on the air, and you don't feel as much heat sitting in your hot car. I have a metalic tint on my wagon and it really makes a difference. It's not mafia-don dark, but does reject mucho heat (and ultraviolet too).

- JimY