The truck is a 4 cyl automatic. Up front I suspected the compressor clutch was malfunctioning. At idle the A/C blows cold. Driving on relatively flat grades at residential or highway speeds all is fine. When I get to a slight or steep grade the autotrans shifts as usual for the grade and A/C stops blowing cold, I still hear the interior fan running and rather loudly. A check of the serpentine belt indicates it is taut. The truck has 80K miles, runs great and never any A/C service or belt replacement. Radiator temp gauge is mid-way. What could cause this?
To add a bit more symptom info what is happening is cold air is transferred from the front vents to the defrost window vent.
Upon searching the internet I have discovered that vacuum operated the controls in the cabin for which vents are in operation. Apparently when I drive up a grade engine vacuum is not held in the line to the control in the dash. Where is the break in the line is still a mystery for me. Totally makes sense as rodents have chewed through my windshield washer hose before. This time probably the vacuum line. From the vacuum canister back to the firewall is where I need to look. Now I need to find the canister.
I think I found the canister under the airbox area. Difficult to get to. I'd like to get to the inside the dash behind the control panel. How does one remove the face on the dashboard?