How do i replace a heater core in a 1999 cadillac deville

SOURCE: 1999 cadillac deville 4.6 heater blowing cold

Besure that you have enough coolant. Your engine has head bolt issues and this allows compression gases into the sooling system, and this pushes coolant out and the heater goes cold before the engine everheats.... VERY expensive to fix correctly. There is a test to determine if exhaust gases are in the cooling system...

SOURCE: thermostat location on a 1999 cadillac deville concours

looked it up online and looks like it's on the front of the water pump in a thing called the coolant inlet housing. one end of it looks something like the letter y and the other end, where the thermostat is round. hope that helps

SOURCE: 1999 cadillac deville air wont work

There's a blower motor (fan) under the hood and up against the firewall near the center of the car that takes some work to remove. It has gone out in the last 2 of my 4 Cadillacs. Turns out if you're not real careful with the positioning of the spark plug wires they will brush up against it, and if one of them gets cracked or brittle it will "arc" and short out the blower motor. The a/c compressor should still come on (you'll hear a click when it engages) but you won't get any air blowing into the cabin, hot or cold.

The part was like $200 stock (year 2000 prices) and it took about an hour to remove it. My Caddy at that time had this damn strut bar going across the engine bay which we eventually removed to get to the blower motor.

SOURCE: How to remove and replace a heater core for a 1998

if I remember correctly the engine has to be removed.

SOURCE: 1999 dodge durango heater core

It's a big job. Drain the coolant down, recover the freon in the ac system and disconnect the lines and heater hoses. Lower the steering column, remove the instrument panel assembly, remove the heater housing. Split the case halves on the housing and there you are. Usually around 500 to 700 dollars at a dealership.