Hey y'all. This is on my 99 Ranger but for what it's worth the A/C system is functionally IDENTICAL to an OBS truck. I figured I'd come here to my old friends for help since this place gets more action than the Ranger forum.

So, pretend I have a 96 F-150. The ambient air temperature is about 90 degrees F. Truck's parked in the shade and the humidity was probably the same as today, about 80 percent. The system is on max blower, full cold, no recirculate (aka "Max A/C", the actuator is broken) with the windows down but the doors closed. Engine RPM is about 1500 (no tach on that truck) and I did not have a fan or any other additional airflow over the condenser other than what the radiator fan was providing. Fan clutch is operational and shroud is installed.

Here's the symptoms. When it's cool out the A/C works fine. Hot summer afternoons, not so great. Problem gets worse when stopped (i.e. low compressor RPM and not much air over the condenser) and if I can stay at speed for awhile, say around 50 MPH or so, cooling returns to acceptable levels. So I put my gauges on and found the readings you see. Does my low side not seem rather low? I do think it's slightly low on charge but with the high side around 250 it doesn't seem that bad. According to my handy chart, at 90 degrees ambient temperature I should see 45-55 low side and 250-270 high side.

What do y'all think? Simply a low charge? Or something that needs a little (or a lot) more work? I think it'll live thru the rest of the summer so perhaps this winter, if it needs any significant amount of work, I'll just throw in a new compressor, accumulator, and orifice tube. And if I find black death I'll flush the lines and evaporator and replace the condenser as well.

 

You have a low charge.
Charge it until the low side is 35psi.

 

Thanks subford, I'll do that and see what happens.

 

and make sure the condenser core is clean

 

How do you determine if it's clean or not?

 

The fins on the outside will be caked with dirt, bugs, or bent bad (use a radiator fin comb or a screwdriver to bend them back, it affects how well the condenser works)

You can buy AC coil cleaner in spray cans at your hardware store. Use the whole can, let it work in, hose down the condenser. Also, a dirty evaporator core affects cooling.

 

to test i will turn ac on and spray cold water into the grill. if ac gets noticeably colder, then i will get into cleaning.
after removing grill first step is blow out from radiator side with air, then water. then i will spray with simple green or another eco friendly cleaner and let it sit hosing it off. if it still looks dirty i will cleaner it again and take a soft bristle brush to the front after letting it sit to soften the crap for a while before hosing off again. on my 02 i saw a 20 degree cooler after cleaning the condenser.

 

Not sure why but I thought you were talking about the inside of the tubes. Thanks.