ok so i have a 1994 f150 with the 5.0 4X4 and my AC will not work my first thought was that she was low on r134 coolant i went and got a few bottles and i hooked up the filler hose and guage on the low pressure side by the evaporator and i am at 30 lbs according to 2 guages when you turn the AC on in the cab my compressor pump clutch will NOT turn on so to fill the system with more coolant i jumped the switch that is screwed into the side of the evaporator and presto the AC compressor turned on and i have cold air.

once the system was cold i thought i needed more r134 so that the sensor on the side of the evaporator would tell the compressor to turn on i put in 2 large bottles of r134 totaling 32oz between the 2 bottles my system is still at 30lbs reading from 2 separate AC guages and still my compressor will not turn on at all (unless i jump the switch on the evaporator) once i do this the AC kicks on and is pretty cold

i also own a 2002 camaro and the AC works in it so just for comparison i hooked the AC guage to it and it reads just under 30

what do you guys think

do i still need more r134 (even after the 32oz i already put in today) ???

do you think that possibly the small sensor/switch that screws into the side of the evaporator is possibly bad??

any input would be appreciated

i could really use my AC lol

thanks in advance

 

it has to be the evaporator i just switched mine over to R134 and i started at zero and it took nowhere near 32 oz so its not the refrigerant

 

Does the pressure equalize after it has been sitting?

 

sounds like a bad pressure switch to me....

 

Replace the clutch cycle switch

 

well "just call me sean" im not sure what you mean by does the pressure eaqualize
the truck sat for over 3 months and it started out with the 30 lbs it is showing
on the guage now. has anyone done one of those pressure switchs before (the switch that screws into the side of the evaporator) do you have to empty the entire system??
is all the coolant going to leak out when i remove it??

 

no it wont leak out there is a Schrader valve on the other side as a check valve just like the inlet ports.

by equalize I am sure he means does the high side and low side pressures even out when it stops cycling?

they should be the same both sides until the AC pump kicks in then the low gets lower and the high gets much higher....

 

o ok i dont have a guage that fits the high pressure side so i have no way to check that but when you turn the air off and the compressor is NOT spinning the pressure on the low pressure side shoots up to like 110 i think
i think im going to replace the switch on the side of the evaporator and see what happens

 

Your pressure going to 110 with the engine off or the compressor not running is exactly what Dr. Bowtie asked. It is best to use a dual gauge set, at least mine has the sight gauge built in so a person can add freon untill the bubbles are gone (old school). Incidentally, the cycling switch has an adjusting screw located beneath the electrical connector. Unplug lthe connector and look inside. Using an ohm meter, a person can adjust the on off setting.

 

well i just installed a new clutch cycle switch on the side of the evaporator and the AC is working great now

thank for the help guys

i just wish i didnt spend $50 on all that free-on now that stuff is expensive now lol