I know this forum is for Volvo, but I have been researching, and ran across your board with some people with experience, so if you don't mind I have a couple questions.
1. I have the Interdynamics ez guage as well, when you are taking a reading, it actually gives you two readings, one when the clutch is on, and one when the clutch is not on. Which reading is correct? I've assumed when the clutch is on reding so far when charging an 89 Mercury Grand Marquis with the R-12 system but no ac.
2. This is a first. The ac is barely cool going down the highway, but at a stop sign it gets pretty cold. I've never had this happen before, and I've charged a couple of systems before, it's always the opposite as described in this thread.
Thanks for your suggestions.
Chris

Question 1) You need to use a jumper wire to keep the compressor engaged at all times during the re-charge. That will eliminate the wild fluctuation in pressure.

Question 2) That is weird. All that comes to mind is more outside air is getting in at higher speed, which would lead me to think there is something wrong with the ducting.

BB