I'll try to make this as short as possible. This is a rear ac truck. Ac Was never right in this truck in the 10 years I've had it.. cooled but not very well. Compressor started to come apart. Shrapnel in lines. Everything is new execpt front evap. Including lines. Evap was flushed thoroughlyVacuum pulled for 4 hrs held for about 20. Charged 3.9 lbs. It was 85 degrees the day I finished it. Low side 45-50 high side 275ish 56 degree air at idle. Drove it for 30 min was very happy with results would hit 52 on the highway. Next day was 98 outside took it for a drive. Air wouldn't get any colder than 68 on highway. Hooked up gauges .low side 80 high side hit 475 before I shut it down. New fan clutch and a furnace fan blowing on it 75/420. 68 degree air.. high side will drop to 350 if I turn rear air off. Any advice would be great!

 

Sounds like line is plugged

 

That is kinda my thought too other than everything is new. Only thing I could think of would be compressor coming apart ??

 

are you sure 3.9lbs is the correct charge amount? seems like a lot. to much refrigerant will cause high pressures in both low and high sides of the system, reduced capacity as the evaporator floods. not sure what build you have but my service info says 3.0lbs for a dual system.

 

Stealership said 4.0. and everything I could find on the internet said 4.. evac the system again tonight put in another orifice tube just because. Recharged to 3.8. Pressures are good but both front and rear air are at 68 degrees...

 

maybe they gave you the wrong info. 99 is a changeover model year. the correct charge level is critical and is something you should rule out. Flooding from overcharge causes the change of state to occur after the evaporator. This results is poor heat exchange. What engine, 99 new bodystyle or 99 old body style