Hello My 89 911 Has high pressor at 350 and does not come down to the same a the low pressor.
high at 350 and low at 100 with 1.7 134 R coolent.
Anyone have a cure for this or what rto do to fix it?
Thanks Alex

 

1) When you observed 350 (psi?) what was the ambient (outdoor temperature around the car) when you noted that pressure?.
2) Was that pressure engine running? Idle. or Engine off? If you are seeing 350 psi with a proper charge on a engine running AC on system
it would have to be 150 F ambient around you, and 100 psi on the low is simply funky.

 

350 psi high side pressure is high, but pressures can approach that if the ambient air temperature is 100°F (38°C) or higher.
Remember that all A/C system pressure measurements should be made with with the engine cover closed and the engine at 2000 rpm.

If this is truly an excessive pressure based on appropriate measurement technique and an appropriate charge level of R134a (approx 38 oz), I would first suspect a blockage in a condenser or (more likely) the expansion valve.