I have a 96 F150 I have had since new and finally this spring the A/C has stopped working. I figured maybe it had leaked a little Freon so I got a can from O'reiliy's (with the gauge, never try it without one). I stick the gauge on the low side by the dryer and it reads 109psi! I guess it isn't low, so before I take it in I was wondering if it is just a blocked dryer or maybe something else. Don't want to be suckered by someone since I don't know any of the mechanics in this area well yet. The pump doesn't engage so I think the overpresure sensor is working. Thanks for any help,

 

I would check your fuse first. Then check the wires going to the clutch on the comprssor using a meter or test light. If no power there, then could be a switch. With your system not running, the freon will equalize thoughout the system. It could be various switches from you selector on the dash, high pressure switch, and the low pressure switch being in open condition.

I'm not an expert on automotive equipment, but I do commercial HVAC/R for a living.

 

I would assume that your compressor was not turning when you put the gage on it. A reading of 109 was just a static pressure and is usually about the same as the temps under your hood so if the engine had been running and the underhood temps were high then that reading was about right. This reading has no relation to the amount of refrigerant in your system. You will need to jump the wire at the low pressure switch on your accumulator to make your compressor run and then see what your reading is. Do not let the compressor run very long if is low on refrigerant as damage will occur.

You need a set of a/c manifold gages that will give you an accurate low and high reading so you really know exactly what is going on. If you do not have gages they can be rented at your local Autozone. You pay for them and when you bring them back they return your money.

 

Thanks for the info everyone. I wasn't sure what the static pressure was supposed to be, the Haynes manual didn't list it. I didn't want to hook up the can if the pressure was that high is why I checked it first. The engine was running and I had just gotten home so it was warm under the good.