Quote:
Originally Posted by E150GT
a mercedes blow out 38 degree temps and a ford blow out 20 degree temps only because the ford has a better design
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20 degree vent temps do not exist in any vehicle. rapid cycling may also be caused by an excessive charge. too much refrigerant is detected by the high pressure switch and the unit short cycles. i'm not saying this is your problem, just making a point.
go to an auto parts store and buy a vent thermometer. put a given amount of water in a container and place in feeezer. get it near freezing - slushy mixture. take it out and drop the the vent thermometer in the slushy solution and let the reading drop. there's and adjustment on the back of the face. maybe an 8mm or so wrench will loosen it. turn and set to 32 degrees; then drop it back in the slushy mix and ensure it reads 32 degress after it's been in there awhile. this is how some hvac guys calibrate their vent temp thermometers.
drive your car 'til it's cooled down with a vent thermometer installed. record temp. all of this is just to provide you with a vent temp.
you'll also need pressure gauges for your vehicle. different types avail. for r134a and r-12. buy whichever you have, then buy "automotive air conditioning basic service training manual" by mastercool, inc. read every page 3 or 4 times. "learn" the principles of a/c before doing real work.
consult this forums search facility. read any/everything on the a/c subject written by arthur dalton. a member here named "jcyuhn" has done a fair amount of serious a/c work and has written/contributed to many good a/c threads. i would search out his posts as well.
low refrigerant is not always the problem. sometimes over-charge is the culprit. people go to places like autozone and buy those all-in-one kits thinking "more is better" and away they go.
arthur dalton's posts will point out key areas to check before doing anything else.
there's more to it than just shooting refrigerant into a system and i'm not accusing you of holding this belief, just making a point.