My '97 ranger xlt 4-cyl (208k miles) is leaking freon - looses enough in a week to trip the low pressure switch inhibiting compressor). In summer of '98, dye was added but they could not find a leak under the hood. They ASSUME it must be the evaporator coil. I keep it charged up but that is expensive - adding freon all the time at $6 per can.

Is there a direct way to determine that the evaporator coil is in fact actually leaking?

It looks like the evaporator coil is located under the hood just in front of the firewall on the passenger's side. The shop estimates $250 labor to replace it (including drawing a vacuum and recharging the system). The parts are about $700, including $480 for the evaporator coil. I want to be sure that the evaporator is leaking beforehand. They say they can't tell with a blacklight because they can't see inside where the evaporator is - is there some way for me to be sure?

 

If you can gain access the core so that you can see it, then maybe you can try the dye test again.

You can get a new OEM evaporator core for around $200 through this site sponsor: http://www.partsguyed.com/

 

But how do I gain access to the core? Does anyone have experience as to what steps you take to get at the core in such a way that you can see if it is leaking? I hesitate to just start taking things apart without knowing what I'm doing.

 

Yokagawa [and others] make a sniffer that can detect halo-whatevers. If they are leaking from the evap, they will be 'smelt' inside the plenums and distribution tubes of the A/C system inside the cab. The sniffer can also smell each of the fittings and hoses, the nose or front seal of the compressor, and so on.
You can buy your own at Harbor Freight, but I don't know how effective it is compared to the brand I mentioned.
Your evap is inside the black box that protrudes into the engine compartment, specifically where the two hoses, the suction and high side, are located. Follow the suction back from the compressor towards the firewall, and follow the high side back from the condenser out in front of the radiator. Where they go through the wall is where your evap is located.
Some trucks need to drop the dashboard to get the plenum out to be able to access the evaporator. Some can be accessed from under the hood.
You can do it yourself if you have the aptitude, and then re-assemble it and IMMEDIATELY take it to be suctioned down and recharged.
This isn't going to be cheap. If you do the work, or have it done, it would be worth while to replace the accumulator, the big 'can' under the hood with the tubes curli-cuing around it. Inside is a dessicant that absorbs any few drops of water or humidity that do not get removed by vacuum. The water will form an acid with the refrigerant & lube, eating the system from the inside out. [that's why it is a good idea to repl the accumulator when you open an 'aged' system]
If there is an oily deposit in the seal on the front of the compressor, it is leaking. Oil or refrigerant or both. Now is the time to fix that. If any of the connectors are covered with a smudge of dirt, they are leaking oil, which stays, and mixes with dust to advise you of the leak. Get and use some Nylog for any fittings you open up. Kind of like magic snot that cannot be removed once you get it in there...
good luck
tom

p.s. You should repost further down the forum in the "HVAC" section for better and more knowledgeable responses.
t