1994 GMC Safari. Rear a/c unit. I want to replace

My first guess would be the master cylinder has failed. Or something is blocking the line to the rear brake cylinders.

you have a plugged radiator or heater line to back heater unit not allowing coolant to flow

if the engine runs good. I would just replace the head gasket, but that is really up to you. it would be a whole lot cheaper if you had a independant mechanic do the head gasket on the vehicle. have a good day !!

Hello,

Here is a detailed summary on the procedure of how to replace the intake manifold gasket on a 1996 gmc jimmy;
REMOVING THE UPPER INTAKE MANIFOLD(PLENUM)
STEP 1 Disconnect Battery (may not be absolutely necessary, but a good practice to avoid shorting a positive wire to ground).


STEP 2 Remove serpentine belt.

STEP 3 Drain the coolant.

STEP 4 Remove air cleaner ducting and disconnect wires.

STEP 5 Disconnect throttle linkage and bracket.

STEP 6 Disconnect cruise control cable.

STEP 7 Remove brake booster vacuum hose at manifold.

STEP 8 Remove PCV hose.

STEP 9 Remove ignition coil and bracket.

STEP 1O Remove purge solenoid and bracket.

STEP 11 Relieve fuel pressure at test port.

STEP 12 Remove fuel lines and bracket.

STEP 13 Remove upper intake manifold.

REMOVING THE LOWER INTAKE MANIFOLD
STEP 1 Remove the distributor and label the spark plug wires.

STEP 2 Remove heater hoses and bypass hose.

STEP 3 Remove upper radiator hose.


STEP 4 Remove EGR valve?

STEP 5 Remove sensors and bracket on right side.

STEP 6 Remove EGR tube, clamp and bolt.

STEP 7 Remove PCV valve (and replace).

STEP 8 Unbolt A/C compressor and move it aside.

STEP 9 Loosen compressor bracket and slide forward, but do not remove it.

STEP 10 Remove alternator bracket bolt (or remove alternator and set aside)

STEP 11 Unplug all vacuum lines from intake manifold.


STEP 12 Unplug all electrical connectors from manifold.

STEP 13 Take note of the intake manifold bolts and mark the location of the bolts.


STEP 14 Remove intake manifold bolts, and manifold.

STEP 15 Clean mating surfaces

THE MAIN INSTALLATION
STEP1 Set the new gaskets in place and apply silicone to flat areas on front and rear of engine block.

STEP2 Apply thread locking compound to manifold bolts.

STEP 3 Install the manifold and tighten bolts to 35 ft-lbs, in proper sequence.

STEP4 Install the distributor.

STEP5 Install the upper intake manifold.



The remaining installation procedures are basically the reverse of removal.


Have a nice day.

get some jack stands then remove brackets for fuel tank lower slightly remove connections vaccum lines and any hoses to tank then drop tank use a flathead or a punch to remove cover to sending unit kinda just screws off.

No,if possible ,remove ac compressor,and move it out of the way,unbolt any hold downs on the ac lines,just move it enough to remove the intake.

Note, removing the upper intake manifold is not necessary when removing lower intake manifold, they are removed as an assembly.
Disconnect negative battery cable. Drain cooling system. Remove air cleaner assembly and inlet duct. Mark and remove distributor. Remove upper radiator hose at thermostat housing. Disconnect accelerator and cruise control cables. Remove heater hoses from intake manifold. Remove EGR pipe.
Disconnect fuel lines at rear of engine. Remove AC compressor and set aside(leave hoses connected). Remove canister purge solenoid. Disconnect theSCPI injector, ignition coil, Ignition Control Module, generator,IAC motor, TP sensor, O2 sensor, Exhaust Gas Recirculation valve and Engine Coolant Temperature sensor wiring harness connectors. Remove PCV valve and hose. Remove lower intake manifold bolts. Remove lower intake manifold.
Installation.
Always use New O-rings when reconnecting fuel lines at rear of engine. Apply a bead of RTV silicone sealer along the front and rear sealing surfaces of the block.See Fig.6. Install new gaskets and intake manifold on block while RTV is still wet to the touch. Use Threadlock 12345382 or equivalent to lower intake manifold bolts. Tighten lower intake manifold bolts in sequence to specification table. See fig. 7. To complete installation, reverse removal procedure.

the knock sensors are located below the intake plenum,or,upper intake manifold as some call it, they screw into the lower intake, the front one is sensor 1, the rear is sensor 2. it is wise to change both if you have some miles.since you are going to be buying a gasket set to do this job.the sensors are cheaper than the gaskets.

there are two gas tank straps on these should be 15mm bolts.
remove the vent tube and fill tube. should be 8mm worm clamps,
once you lower the tank about half way remove the 2 connectors to the fuel pump and all 3 of the plastic fuel lines. to remove the lines there will be tabs on the ends that need to be pushed in for them to release. its not really hard its just uncomfortable on the ground.

once the lines and wires are removed lower tank all the way. fuel pump is held in my a ring that spins or unscrews. you may need to tap it with a pry bar on the metla tabs.

make sur to line up th O-ring and if it comes with new conectors replace them. alot of the connectors go bad.

Hope that helps,
Michael
PLZ rate

remove catalitic converter or might need to replace the upper intake gasket.