Diagnosis And Testing; Vacuum Control System - Jeep KJ 2005 Service Manual

24 - 18 CONTROLS
A/C HEATER CONTROL (Continued)
Fig. 15 A/C-Heater Control - Typical
1 - REAR WINDOW DEFOGGER SWITCH
2 - BLOWER SPEED CONTROL
3 - MODE SELECT CONTROL
4 - TEMPERATURE SELECT CONTROL

DIAGNOSIS AND TESTING

VACUUM CONTROL SYSTEM

Vacuum control is used to operate the mode-air
doors within the HVAC housing. Testing the opera-
tion of the heating-only and heating-A/C system
mode control will determine if the vacuum and
mechanical controls are functioning. However, it is
possible that a vacuum control system that operates
correctly at engine idle (high engine vacuum) may
not function properly at high engine speeds or loads
(low engine vacuum). This can be caused by leaks
within the vacuum system, or a faulty vacuum check
valve.
A vacuum system test will help to identify the
source of poor vacuum system performance or vac-
uum system leaks. Before starting this test, stop the
engine and make certain that the problem is not a
disconnected vacuum supply line at the engine intake
manifold vacuum tap or at the vacuum reservoir.
Use an adjustable vacuum test set (Special Tool
C-3707-B) and a suitable vacuum pump to test the
HVAC vacuum control system. With a finger placed
over the end of the vacuum test hose probe (Fig. 16),
adjust the bleed valve on the test set gauge to obtain
a vacuum of exactly 27 kPa (8 in. Hg.). Release and
block the end of the probe several times to verify that
the vacuum reading returns to the exact 27 kPa (8
in. Hg.) setting. Otherwise, a false reading will be
obtained during testing.
Fig. 16 Adjust Vacuum Test Bleed Valve
1 - VACUUM PUMP TOOL C-4289
2 - VACUUM TEST SET C-3707
3 - BLEED VALVE
4 - PROBE
VACUUM CHECK VALVE
(1) Remove the vacuum check valve. The valve is
located in the vacuum supply line (black) at the
HVAC system vacuum tee.
(2) Connect the test set vacuum supply hose to the
A/C-heater control side of the vacuum check valve.
When connected to this side of the check valve, no
vacuum should pass and the test set gauge should
return to the 27 kPa (8 in. Hg.) setting. If OK, go to
Step 3. If not OK, replace the faulty vacuum check
valve.
(3) Connect the test set vacuum supply hose to the
engine vacuum side of the vacuum check valve.
When connected to this side of the check valve, vac-
uum should flow through the check valve without
restriction. If not OK, replace the faulty vacuum
check valve.
A/C HEATER CONTROLS
(1) Connect the test set vacuum probe to the
HVAC vacuum supply (black) line at the tee in the
engine compartment. Position the test set gauge so
that it can be viewed from the passenger compart-
ment.
(2) Place the A/C-heater mode control in each
mode position, one position at a time, and pause
after each selection. The test set gauge should return
to the 27 kPa (8 in. Hg.) setting shortly after each
selection is made. If not OK, a component or vacuum
line in the vacuum circuit of the selected mode has a
leak. See the procedure in Locating Vacuum Leaks.
KJ