All winter I've had the dreaded steamed up oily windows from running my defrost. I just assumed it was the heater core and that's going to be a bear to change. However a friend at work with a 01 cummins has the same problem and thinks it is the ac leaking. We both have some thing leaking from the floor vent. I thought it was dirty antifreeze but he says it's more oily coming from the ac. Sometimes I think it smells like antifreeze but then yet it doesn't. He put in 2 cans of 134 and a stop leak to see if it fixes it. So I remembered I had to charge mine twice last summer. so it was pushing 60 degrees today so I tried my ac it never got cold. So should I try some stop leak or go right to taking out the dash and changing the evaperator and heater coil? Anyone else have the steamed up window problem?

Here is how to do it.

http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/27-hvac-heating-ventalation-and-air-conditioning/57-air-conditioning-evaporator-core-heater-core-replacement

 

As far as I know on these trucks, the defrost mode is actually just the AC running to suck the moisture out of the air. Back in the day, the defrost mode just meant fresh air instead of the recirculated air coming in. Someone correct me if I am wrong here though. I can always tell when I need to top off the R134a because my windows will start fogging up.

It doesn't really matter, if your pulling the box replace both of them.

So i must have a leak if I need to ad the 134a.

Now the question is, Where is the leak? So if I was in your shoes I would by a can of freon with the dye in it. Now run the A/C for a good 5-10 mile trip. Then park the truck in a shade or dark shop. Grab a black light and go hunting for the dye. Majority of the system you should be able to view under the hood. Now as for evaporator that is the only piece you have to remove from the box to see. So if nothing pops up under the hood then most likely a evaporator issue. You might find the tell tale signs of greasy parts too.