Originally Posted by leathermang

How long had the AC system been turned off when you got that reading ?
There is the possibility you only need topping off with R12..

HOWEVER, you do not have enough info to do that yet...

You are going to need to check the vent temperatures with a pencil thermometer..about $5 ..... while making sure the test conditions are correct...
and then hook up the gauges to both the high and low sides and see what readings you get...

The specs for the test have been given lately.. from memory----.. one of the more important is having a good fan blowing right into your condensor.... and being at high idle, windows OPEN.... set on MAX AiR.... clean the condensor AND radiator fins ... of course this has to be done outside.... carbon monoxide from your exhaust is deadly in small amounts....