I have a 94 gt 5.0 i just installed a NEW ac compressor as the old one blew front seal. also replaced accumulator, condensor. The ac works great for about 25 minutes then i have to switch if from max ac to vent to thaw the evap. The liquid line coming out of the evap is freezing the hose about a quarter the way down. I am wondering if the orifice tube is blocked or if i have a problem with the evap. No leaks anywhere in system after i thaw the evap it works just fine for another half hr or so can someone point me in the rite direction. I am thinkin i need to replace the liquid line that has the orifice tube in it. But maybe someone else can give me a little more info. Also replaced high pressure cutout switch and low pressure switch the ac does not cycle the compressor ALWAYS runs. It will even turn on if there is no freon in system. Maybe there is a control module somewhere that needs to be replaced please help.

 

if there is a restriction in the system you'll be able to see it on the gauges, system will go into a vaccum on the low side or spike on the high side pending where restriction is.....what are your pressures reading at idle and at 2500 ish??

 

2500 35-40 on the low and 300 on the high. i am thinking that the compressor should be shutting off at 275 according to alldata but i could be wrong.

idle is 45-50 low and 225-240 on high side

 

300 on a 134 system is way to high and 35-40 on low is a little high also......how did you determine correct amount of refigerant to add?? did you use a professional machine to disperse proper amount?? not sure what year 134a started but if your system was originally r-12 that was converted to 134a remember that a system that was originally r-12 when converted to 134a you now use 80 percent of the r-12 amount to determine the amount of 134a to add...sounds like the system may be a little overcharged.....I assume your fan is coming on to pull air across the condensor??

 

this car did from the factory come with r134 yes used a snapon ac machine vacummed system for 20 min let sit for 30 min to verify no leak. Charged system to 2.13 lbs as per alldata is the freon capacity for the car. i am thinking it is a controller issue i have already replaced all sensors and has a new compressor with new clutch. Its not shutting the compressor off at 275 which is what it should be cycling at 275 should activate high pressure switch to disengage clutch until pressure drops below 250 psi on high side. so i am just confused. The reason i have come up with for the freezing is because the compressor is constantly on and not allowing the pressure to come down thus forth freezing the liquid line coming out of the evap going to the condensor. freezes half way to condesor rite where the orifice tube is. This orifice tube is built into liquid line and is easier to change whole line at 30 bux vs trying to change the orifice tube but this does not explain why my compressor is not cycling like it should. or do all mustang ac compressors just keep the clutch engaged all the time.

 

the only control module or more so panel present in the system is the control panel inside the car, your system is not that advanced as are today's cars are where a/c function is managed via modules over a CAN system.........ANYWAY, if you can see WHERE THE FREEZING STOPS, OR STARTS, I'd replace the orifice line first, make sure the condensor and radiator fins are free of all debris ....... unless outside temps are in the mid to upper 90's it's rare the 134a system will cycle off as a result of high side getting to high as long as fan and condensor are working, that is what'll drop high side down, I work on these systems all day long and unless it's deathly hot out the high sides on 134a systems tend to run in the 180 to 210 range max and when they get up to 250+ either there is a restriction, system is overcharged with refrigeratn or oil, or the condensor is plugged with debri or fan is not doing it's job

 

your most likely gonna have to release the freon and recharge it to 32 oz. of 134 and 8 oz. of oil