a/c cools great in city or short drives (60 miles or less). any distance over this it quits cooling. i am almost sure it is freezing up. it has correct amount of freon in it. if it is freezing up what shuts compressor off & on when desired temp is reached? what else would cause these problems?

 

without more info on ambient temperatures and some other details like vent temp and high and low side pressures i can't really help you much. i am a certified tech and i do a lot of a/c work in the summer months, and R134-a is highly regulated in canada you need a license to buy it and handle it here. and how do you know it has the correct charge of freon in it? tell me if there has been any work done to the a/c system/or front end collision repair (sometimes you may not have known about work done to your car in the a/c system).

if you know for sure it has the correct charge there are a couple easy things to check for...
1. the compressor clutch could be weak.
2. the relay could be weak.
3. your cabin filter could be clogged up with dirt and not alowing air flow through the evaporator.
4. H block could have a restriction.
5. there could be too much oil in the a/c system.
6. the pressure sensor could be faulty.
7. the condenser could be blocked off by ????
8. the engine temp sensor could be indicating an over heating condition (not likely but its a possibility)
9. shorts to ground or wiring problems

give me some feed back and i'll try to help you but i need some or all of the earlier mentioned info to do it without seeing the car in person.

 

i also am certified. (thermo king tech) ambient temp around 80, vent temp 45 when in city or driving under 60 miles with out stopping. after driving more than 60 miles vent temp goes up to around 70. i have recovered freon from system replaced accumlator & pulled a 500 micron vacuum & it held. i then charged with the correct amount of r134a per sticker on firewall. low psi is between 15 & 20 & high side is 200 to 300. i bought car new no repairs or wreck damage.after you leave a/c off for about 30 to 40 minutes it will cool again, then repeats the same problems.

 

okay for that ambient temp your high side is good but the low side is too low it needs to be around 25-35 psi and as high as 45 when the compressor cycles. it sounds like there is still a low charge or possibly contaminated refrigerant. and make sure your pressure sensor on the dryer isn't contaminated with oil leaking from the shrade valve. when you pulled the vacuum it needs to see as close to 30 in/hg for about an hour to evaporate all the moisture in the system. and if you are using recovered R-134a make sure you aren't accidently getting any other types of refrigerant in with it.