Dodge RAM TRUCK 1500 1995 Service Manual page 1681

24 • 12 HEATING AND AIR CONDITIONING
MHATING
AMD MR
C O N D I T I O N I N G
TEST
P R O C E D U R E S
INDEX
page
Air Conditioning Cycling Switch 13
Blower Motor 12
Compressor Clutch Test 14
VACUUM CONTROL
This control is used with the heater and A/C sys­
tems.
Use an adjustable Vacuum Test Gauge (C-3707)
and a suitable vacuum pump to test heater-A/C con­
trol vacuum. With a finger placed over the end of test
hose (Fig. 1), calibrate vacuum control valve on the
test gauge to obtain -27 kPa (8 in. Hg.). Release and
block the end of the test hose several times to verify
vacuum setting.
BLEED VALVE J9324-75
_ Fig. 1 Adjust Vacuum Test Bleed Valve
VACUUM TESTING THE ONE-WAY CHECK
WAIVE
(1) In the engine compartment, disconnect the
Heater-A/C vacuum supply (black) hose. This hose
passes through an opening in the dash panel.
(2) Remove the vacuum check valve. This valve is
located on the (black) vacuum supply hose at the in­
take manifold.
(3) Connect test vacuum supply hose to the
HEATER SIDE of the valve. In this direction the
gauge should return to calibrated setting. If valve
leaks vacuum in this direction, valve replacement is
necessary.
(4) Connect test vacuum supply hose to the EN­
GINE VACUUM SIDE of the valve. Vacuum should
flow through valve.
page
High Pressure Relief Valve 14
High-Pressure Cut-Off Switch . . . . . . . . . . . . . . . . 14
Vacuum Control . . . . . . . . . . . . . . . . . . . . . . . . . . 12
VACUUM TESTING THE HEATER-A/C
CONTROLS
(1) Connect the test vacuum probe to the vehicles
(black) vacuum supply hose. Position vacuum test
gauge so it can be viewed from the passenger com­
partment.
(2) Position the heater-A/C control mode selector to
DEFROST, FLOOR, Bl-LEVEL, PANEL or RECIRC
(with A/C). Pause after each selection. The test gauge
should return to the calibrated setting of -27 kPa (8
in. Hg.) after each selection is made. If the gauge
cannot achieve the calibrated setting, a vacuum cir­
cuit or component has a leak.
LOCATING VACUUM LEAKS
To locate a vacuum leak, disconnect 7-way vacuum
connector behind the heater-A/C control panel (refer
to Heater-A/C Control Panel Removal/Installation).
Connect the calibrated vacuum hose probe to each
port in the vacuum harness connector (Fig. 2). After
each connection is made, the test gauge should re­
turn to calibrated setting. If all circuits function
properly, replace heater-A/C control. If not, determine
the color of the vacuum circuit that is leaking. To de­
termine vacuum line colors, refer to the Vacuum Cir­
cuits Chart for the heater and A/C housings.
Disconnect the vacuum actuator at the other end of
the circuit. Instrument panel removal may be neces­
sary to gain access to some components. Block the
end of the disconnected vacuum line. The test gauge
should return to calibrated setting. If not, that circuit
has a leak and must be repaired or replaced. If test
gauge returns to calibrated setting, the vacuum ac­
tuator must be replaced.
BLOWEft MOTOR
Power to the blower motor is supplied from fuse #1.
The blower speed is controlled by the blower switch
and blower resistors. With the switch in LO, the
ground circuit is supplied to the motor through all of
the resistors (Fig. 3). When the blower switch is
moved to a higher speed, the ground increases to the
motor which increase the blower speed. This is ac­
complished by bypassing some of the blower resis­
tors. When the switch is in HI, all blower resistors
are bypassed and the ground circuit is applied di­
rectly to the blower motor.