So about a month ago, my preacher fainted due to the 100 + degree days, while driving around doing errands due to the ac not working. Since I used to work on vehicles, I offered to take a look and lent him my F-150 to use while I did that. That was a couple weeks ago. Things have been busy around here, and I have the old 350 to drive, so I didn't get around to it until today. Hooked up the gauges and found the pressure low. Evacuated and did a vacuum test. It failed with in 5 minutes. Yes, I do happen to have an OLD r134 machine laying around, guess being a pack rat pays off some days. Added some dye and a little charge enough to get the compressor to cool some and stay on. Looks like everything is working for the front system at least. Didn't actually check to see if the rear was cooling.

So I'm waiting for the the pressures to equalize and for the dye to start showing. However, I do have a question. Where is the rear evaporator located on a 98 Expy? From what I've read around here. The front runs of a expansion valve, the rear of an orifice tube, the lines really run under the truck? Was hoping it would be a condenser or compressor, but just want to know where to start looking when (and if) i can find that stupid black light.

Thanks in advance,

 

Behind the rear wheel well, driver's side.
Other way around.
Yes.

Start inspecting anywhere there is a joint. O-ring failures are common. Compressor front shafts leak, manifold seals leak, I've even seen a compressor leak at the seal where the halves are joined together.

Good luck!

 

Thanks, that's really helpful! I'll report back with findings. Much appreciated!

 

Especially check the connection right there at the compressor. Those pipe O-rings take a lot of heat right there, and very common leak area. A can of brake cleaner comes in real handy for cleaning off an area for inspection or work.
If you need a good UV flashlight, Lowes has a little Craftsman UV flashlight that's real handy for about $10 .

Craftsman UV Flashlight at Lowes

 

I just grabbed a little one from Harbor Freight. It was about 8$ didn't realize Lowe's had a Craftsman. First preliminary inspection showed no dye. I remember that about dye though. Some times it takes a long time to show where the leak is. I'll recheck the connections on the compressor again though. Appreciate the heads up!

 

Here is the rear AC layout for a 1999 which should be similar to your 1997.