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This bulletin supersedes TSB 24-01-96
Models: 1994-1996 BR Ram truck
1993 - 1997 (ZJ) Grand Cherokee
1996 - 1997 (ZG) Grand Cherokee (international Markets)
1994-1996 (BR) Ram truck
The vacuum supply to the Heater A/C System may drop when accelerating or when speed control engages. This may cause the mode vacuum motor to switch to the defrost position.
Use the procedure outlined in the appropriate Service Manual (Group 24) to verify that the Heater A/C system does not have any vacuum leaks. If no leaks found, perform the Repair Procedure.
AR NPN Appropriate Size Vacuum Hose
This bulletin involves installing an additional vacuum check valve.
Locate the vacuum source line to the Heater A/C system in the engine compartment (Figure 1, Figure 2). Install the vacuum check valve in the Heater A/C system vacuum line. Make sure that the check valve is installed to allow vacuum to pass into the Heater A/C system, but block any vacuum drop when accelerating.
NOTE: DO NOT INSTALL THE VACUUM CHECK VALVE IN THE VACUUM LINE GOING TO THE RESERVOIR OR THE SPEED CONTROL SERVO. INSTALLING THE VACUUM CHECK VALVE IN THE LINE GOING TO THE VACUUM RESERVOIR OR THE SPEED CONTROL SERVO WILL HAVE A NEGATIVE EFFECT ON THE SYMPTOM / CONDITION AND POSSIBLY CAUSE THE SPEED CONTROL SYSTEM TO DROP VACUUM WHILE ACCELERATING.
POLICY: Reimbursable within the provisions of the warranty.
TIME ALLOWANCE: Labor Operation No: 24-50-47-91 0.2 Hrs.
FAILURE CODE: P8 - New Part
Now I will attempt to describe figure 1 and 2, Figure 3 applies only to the Grand Cherokee.
Figure 1: A sketch of the passenger side firewall near the auto trans dip stick. The vacuum line is shown coming from behind the valve cover through a "T" fitting and into the cowling above the fire wall (just below the windshield wipers) to the vacuum reservoir through an "L" fitting attached directly to the straight through part of the "T". Attached to the leg of the "T" fitting another vacuum line is routed to the firewall and into the cab (to the HVAC control panel), it appears to enter through the same boot as the A/C lines. About halfway between the "T" and the firewall is a note to "Install Check Valve Here".
Figure 2: A diagram of the installation of the check valve as opposed to the physical layout described above.
A FOLLOWUP FROM Mikie
I checked my `94 and it is pretty much the same way as described for the Jeep. The original check valve is at the manifold end of the vacuum lines. It has a larger hose than the ones going to the reservoir. I don't know what size or how much the one they specify is, but I know a NAPA 2-1015 has about the right size ends to match the lines going to the Heater A/C system line. It costs $4.98 and PEP Boys has a #03308612552 for $4.79 that is the same one.
Thanks to Darin Brummett and Bob Bergevin for supplying this TSB information
This page was edited on: May 3, 2004