How do you replace a heater core in a 1991 Cadillac Deville? What all has to be removed in order to remove the heater core? What does the heater core look like and how costly is this if taken to a shop?

you must remove the clamps from the heater core from the engine compartment and the covers from under the dash to be able to remove the heater core

Not sure if this will help but this is on a 2001 Eldo which should be close to what you have. I would also suggest the library and check out a Chilton's repair manual for you car.
Heater Core Replacement 2001 Eldorado Archive Cadillac forums Cadillac...

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First, according to the manual, disable the SIR system

Fuse panel in trunk behind back seat driver's side

Connection to left of steering column

Remove glove box
and unplug second SIR connector

Then remove bottom insulator panel and disconnect battery
HVAC programer can be pulled out of it's plastic cradle and then the top and bottom air door actuators must be removed

Then just two screws and you have the heater core uncovered.

You will need a repair manual for your Cadillac. On some cars, the core is accesible without removing the heater case from car. On cars where you have to remove the case to replace core, it can get to a real pain point. There are some cars that require the whole dash to be removed first, before the heater case and core can be gotten to. Hope for the best-and get the manual. Libraries also have good reference/repair sources.

If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core.
When a heater core leaks, a new heater core is installed or the old one repaired.
Heater Housing

• The heater housing is usually under the dash and must be removed to gain access to the heater core.
• Procedures for replacing the heater core vary with the year, make, and model of car. It threfore necessary to consult the manufacturer's repair manuals for the proper procedure for replacement.

The heater housing is disassembled to get to the heater core. Heater Core

• Remove the access panels(s) or the split heater/air conditioning case to gain acess to the heater core.
• Remove the heater coolant hoses.
• Remove the cable and/or vacuum control lines (if equipped).
• Remove the heater core securing brackets and/or clamps.
• Lift the core from the case. Do not use force. Take care not to damage the fins of the heater core when removing.
• To reinstall the heater core, reverse the removal steps.

When the heater core leaks and must be repaired or replaced, it is a very difficult and time-consuming job primarily because of the core's location deep within the firewall of the car. For this reason always leak test a replacement heater core before installation.

Hello,

Here is detailed solution on how to replace the heater core in the 1999 cadillac deville;



STEP 1 Disconnect the negative battery cable.


STEP 2. Drain and recycle the engine coolant.

STEP 3. Disconnect the heater core hoses using tool J-37097 or an equivalent.

STEP 4. Remove the right side sound insulator and the glove box module.


STEP 5 Remove the programmer shield, if equipped, and disconnect the air mix valve link.

STEP 6 Disconnect the programmer vacuum and electrical connectors.

STEP 7 Remove the heater core cover, leaving the programmer attached.


STEP 8 Remove the heater core retaining screws and the heater core.



have a nice day..

This will require to remove the dash to get access to the heater core. After the whole dash is apart access to the heater core is easy and self explanatory

i was surrounded by smoke in the inside of the car while i was driving the car started to overheat and antifreeze poured into the inside passeger side of my car is it the heater core and is it exspensive?

I had the same problem in my 1991 caddy, and turned out to be the blend door. It is located in back of the glove compartment. There are two kinds, the automatic blend doors and the manuel ones. Since the temperature is automatic and programmed to stay where it is set, it would be an "automatic blend door". Not a hard fix...

I do think you have to pull he dash, for that you will need a manusl, try ebay for used factory manuals, I have had good luck getting them there for all my cars.