I need to remove the evaporator core from my truck.

87-94 C-1500
REMOVE OR DISCONNECT

Battery ground cable.
Coolant from the radiator.
Refrigerant from the system.
Coolant overflow tank.
Heater hoses from the coil tubes.
Refrigerant inlet (45) and discharge (46) lines from the evaporator.
Electrical connection to the temperature actuator.
Heater case bottom plate (50).

Remove the seven screws that hold the bottom cover.

Heater core.

Remove the screws and brackets that hold the core to the case.

Evaporator core cover (51).

Remove the four screws that hold the cover to the evaporator case.

Evaporator core.

Pull the core out and down from the evaporator case.

INSTALL OR CONNECT

Evaporator core.
Evaporator core cover (51).

Install the four screws.

Heater core.

Install the three screws and bracket.

Heater assembly bottom plate (50).

Install the seven screws.

Electrical connection to the temperature activator:
Refrigerant inlet (45) and discharge (46) lines to the evaporator.Tighten to;

Inlet (45) line connection to 41 Nm .
Discharge (46) line connection to 24 Nm .

Heater hoses to the heater core (47).
Coolant overflow tank.
Refrigerant to the system.

Leak test.

Coolant to the radiator.
Battery ground cable.

take your time. is a lot of work but is not that bad.

Here a guide for dong a heater core, not the same part, but in the same location. It may help you see what you are in for

https://www.2carpros.com/articles/replace-heater-core

Roy

See the image below for an exploded view of the HVAC plenum