I have a 99Expy EB 2wd. I want to know where is the low presure valve located. Is it the one by the radiator on the passenger side. It has a black cap on it. Is so let me know. Thanks.

 

I don't know, I have a 92 F150, be careful you may be looking at the fuel line test port. Traditionally, red is high, blue is low. The low side "port" is usually near the accumulator and your cab evaporator, these components are in the low pressure side of the system as these are after what is known as the orifice tube.
Basically, high pressure exists in the compressor output and hose, condensor and hoses, and up to the orifice tube, the orifice tube is not a recognizable feature except it may be indicated by a machining crimp in one of the tubes leaving the condensor.
The evaporator is usually hidden away in the blower box, it is the device that cools the cab. The accumulator should be visible, and it may look like a big capsule and should have an electrical connector with two wires coming from it. The low side port should be near one of these components or just upstream or downstream as you follow the AC lines.

 

2000 Expy 2wd.....I just had mine worked on and the low side was in the back towards the fire wall. WARNING!!! I thought my freon was low and it turned out to be over filled. Anybody know any good AC guys in the Raleigh NC area?? at a fare price?

 

As 924X2150 had said, it is on the accumulator. Stand on the passenger side and look at the firewall. There is an electrical box hanging on the firewall, look underneath for the accumulator (the low pressure port is right on it). It is real tight unless you have tiny hands. Better to move the electrical box a bit to gain clearance. If you are refilling yourself, make sure, at the least, you get a refill kit with the gauge attached so you don't overfill (overpressurize) the system.

By theway, what you were looking at is the high side port.

BigMan69

 

Look on the passenger side, near the firewall. There maybe a hose blocking your view. I can't remember if its near or on the accumulator but if you find the accumulator then the service valve is right there. The accumulator is a silver oblong shaped device attached to the firewall.

 

Thanks for all your input. I will go now and look for it. Thank you