Check for a plugged evaporator remove fan motor under hood and see if evaporator is plugged
when you go through deep water
Behind the rear seat, access through trunk.
Since a Cadillac DeVille is quite an old car, it is hard to find parts for the vehicle. However, some people sell the old parts on eBay or through a local auto shop.
One can purchase parts for a 1998 Cadillac Deville at Canpar, UAP, AutoTrader Magazine, directly through any authorized GM dealership, and at most local junkyards or scrap works.
A 1990 Cadillac Deville air conditioner should hold 46 oz. R12 Freon. This should be verified through the owners vehicle manual.
The cabin air filter on a 1991 Cadillac DeVille is located under and slightly behind the glove compartment. All the air which enters the cabin is filtered through it to remove most contaminants.
Transmission fluid is always put in through the Tranny dipstick tube.
I've repalced a fuel pump in a 94 Cadillac STS and it required removal of the gas tank. The sending unit is on top of the tank.
you can get it through the auto zone website it's free to sign up
It appears so much bigger you probably won't recognize it as an "a".
e.g. heater core clogged is a common one - flush or replace it
Most likely a the engine is eating it through the head gasket if its a small amount tiny dont worry about it its just condensation in the muffler.