System Low; Vacuum System; Vacuum Check Valve; Heater - A/C Controls - Jeep 200 Cherokee Service Manual

24 - 18 HEATING AND AIR CONDITIONING
DIAGNOSIS AND TESTING (Continued)
(2) Connect and dispense 0.283 kilograms (0.625
pounds or 10 ounces) of R-134a refrigerant into the
evacuated refrigerant system. See Refrigerant Sys-
tem Charge in this group for the procedures.
(3) Position the vehicle in a wind-free work area.
This will aid in detecting small leaks.
(4) With the engine not running, use a electronic
R-134a leak detector and search for leaks. Because
R-134a refrigerant is heavier than air, the leak detec-
tor probe should be moved slowly along the bottom
side of all refrigerant lines, connector fittings and
components.
(5) To inspect the evaporator coil for leaks, insert
the electronic leak detector probe into the center
instrument panel outlet. Set the blower motor switch
to the lowest speed position, and the mode control
switch in the recirculation mode.

SYSTEM LOW

(1) Position the vehicle in a wind-free work area.
This will aid in detecting small leaks.
(2) Bring the refrigerant system up to operating
temperature and pressure. This is done by allowing
the engine to run with the air conditioning system
turned on for five minutes.
(3) With the engine not running, use a electronic
R-134a leak detector and search for leaks. Because
R-134a refrigerant is heavier than air, the leak detec-
tor probe should be moved slowly along the bottom
side of all refrigerant lines, connector fittings and
components.
(4) To inspect the evaporator coil for leaks, insert
the electronic leak detector probe into the center
instrument panel outlet. Set the blower motor switch
to the lowest speed position, and the mode control
switch in the recirculation mode.

VACUUM SYSTEM

Vacuum control is used to operate the mode doors
in the heater-only and heater-A/C housings. Testing
of the heater-only and heater-A/C mode control
switch operation will determine if the vacuum, elec-
trical, and mechanical controls are functioning. How-
ever, it is possible that a vacuum control system that
operates perfectly at engine idle (high engine vac-
uum) may not function properly at high engine
speeds or loads (low engine vacuum). This can be
caused by leaks in 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 tube at the engine
intake manifold vacuum tap or at the vacuum reser-
voir.
Use an adjustable vacuum test set (Special Tool
C-3707-B) and a suitable vacuum pump to test the
heater-A/C vacuum control system. With a finger
placed over the end of the vacuum test hose probe
(Fig. 9), 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. 9 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 tube (black) at the
heater-A/C system vacuum tee.
(2) Connect the test set vacuum supply hose to the
heater-A/C control side of the 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 valve.
(3) Connect the test set vacuum supply hose to the
engine vacuum side of the valve. When connected to
this side of the check valve, vacuum should flow
through the valve without restriction. If not OK,
replace the faulty valve.
HEATER-A/C CONTROLS
(1) Connect the test set vacuum probe to the heat-
er-A/C vacuum supply (black) tube at the tee in the
engine compartment. Position the test set gauge so
that it can be viewed from the passenger compart-
ment.
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