1991 air conditioning problem

System was changed from R12 to 134A 2 years ago. Has worked fine up until the past 30 days. Now low pressure side has a high pressure reading. Only cools when care is moving, when car stops air warms up. Electric fan is running, compressor is running. Looking for any input as to whether this could be a dryer problem. Thanks.

no if it was the low would be really low and the compressor would be kicking on and off sounds like a bad compressor or vacuum leak going to the controls .when sitting vac is high when driving down the road vac is low. and the control doors would do weard things .