I'm sure there has already been a post on this but I can't find it. I hve a 96' Ranger 4.0 5 speed. While driving, if I put the truck under a load such as going uphill or towing, the air conditioner fades out and blows warm air. Once I start downhill the air will come back on. It is much worse when towing. Any ideas? Thanks.

 

See FAQs above. Your system is very similar.

 

Check for vacuum leaks. It isgoing into defalt because the vacuum is not able to hold the door open. Check the reserve can, it may be rusted out, or damaged.

 

My biggest problem is that I can't find the vacuum lines that are for the air conditioner. I don't know where to check.

 

I currently have the same issue on a 2000 E-350 (V10) passenger van. I also owned a 1994 F-150 (i6) super cab that had this problem. I took the F-150 to an Auto A/C shop, and ~$350 later, supposedly going through all the vacuum lines and swearing there were no vacuum leaks, it still wasn't fixed. I would think that this is a more common problem than a search here would indicate. Anyone else with other/more input?

 

I would have to say vacumm leak as well. My current truck and the 94 F150 I had before it would do pretty much the same thing, but it would change from vent to defrost, then let off the gas and it would switch back. I don't know about Rangers, but the problem on mine has always been the lines on the passenger side near the firewall. They are the little white 1/8" lines, and they just get brittle and crumble in places. I just found some small hose that would fit over them fairly tight then cut out the bad section and just pushed the old hose into the new section or you could just replace entire length of existing hose, but I found some have molded on rubber connectors on the ends.

TC

 

If it isnt a vacuum leak causing the system to go into default mode (defrosters work but not out vents) then your compressor could be shutting down from wide open throttle relay. This would be normal to allow the extra power to pull the hills under heavy load. It may be that your engine is heavily worn or needs serious tune up work and has very little power left so you are having to hold the throttle open to pull the hills causing the WOT relay to disengage the clutch.