26
Genuine OEM Parts 1.800.233.4823 www.morganolsonparts.com
27
USPS 2 Ton Delivery Vehicle 2016 - 2018 Models
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POSSIBLE CAUSE #3
~ Control Panel Selector Switch is defective
CORRECTIVE ACTION
~ With the ignition turned to Accessory, unplug each of the connectors from the Plenum servo
motors and test according to the information in the
Electrical Connection To Plenum Servo Motors Diagram
. If the
test fails to find agreement with the
Diagram
there is a good possibility that the Mode Selection Switch at the control
panel is defective. Replace the Mode Selection Switch.
Air temperature cannot be controlled
POSSIBLE CAUSE #1
~ Water valve not operating
CORRECTIVE ACTION
~ Valve may
not be receiving a signal from control
panel, or valve is defective. Discon-
nect the electrical connector from the
valve. With the ignition switch turned
to
Accessory
, check for the presence
of 12 volts between the red wire (+12
V) and the white wire (ground) as not-
ed in the
Water Valve Electrical Dia-
gram
. The yellow/red signal wire will
p12 V (full cold position) drop-
ping to zero volts (full hot position) as
the temperature control knob is rotated
clockwise. If the condition at the con-
nector is in agreement with the
Dia-
gram
, proceed as follows:
Step 1 Disconnect the water valve
from the 5/8” heater hoses,
Step 2 Carefully inspect the four
small terminal pins on the motor, make
sure that they are not damaged,
Step 2 Reconnect the valve to the
electrical connector,
Step 3 Rotate the Temperature Con-
trol Knob and watch for any response
from the valve,
Step 4 If no valve rotation is ob-
served, replace the valve.
POSSIBLE CAUSE #2
~ Water valve not electrically connected
CORRECTIVE ACTION
~ Disconnect the electrical connector from the valve. With the ignition switch turned to
Acces-
sory
, check for the presence of 12 volts between the red wire (+12 V) and the white wire (ground) as noted in the Water
Valve Electrical Diagram. The yellow/red signal wire will p12 V (full cold position) dropping to zero volts (full hot
position) as the temperature control knob is rotated clockwise. If none of these conditions exist, refer to the
Wiring Dia-
gram
and examine the system’s wire harness for any loss of continuity. Repair as required.
,
A/C system not providing cool air
POSSIBLE CAUSE #1
~ Loss of refrigerant
CORRECTIVE ACTION
~ Verify the presence of 1.75 pounds of refrigerant R134a. If the AC system is either partially
low, or completely empty, a search will be required for leakage. Replace and repair as required.
POSSIBLE CAUSE #2
~ Compressor not engaged
CORRECTIVE ACTION
~ Confirm that the system is fully charged. With the ignition switch turned to
Accessory
, the
blower switch turned to the highest speed and the AC (blue) rocker switch engaged, proceed as follows:
Step 1
: Check for the presence of 12 volts at the compressor. If yes, make certain that the compressor clutch is fully
grounded. If the ground circuit is intact, the compressor clutch has, most likely, failed and requires replacement.
Step 2
: If no voltage is present at the compressor clutch, refer to the
Wiring Diagram
and check for voltage at each of
the system pressure switches.[
Note
: The low pressure switch is located on the suction hose near the firewall and opens
on a pressure drop to 8 psi. The binary (high/low) pressure switch is located on the liquid hose near the receiver/drier
and opens on a pressure rise to approximately 400 psi and a pressure drop to 28 psi.] With the system fully charged,
there should be continuity through both switches. Replace as required.
Step 3
: If no voltage is present at the pressure switches, check for voltage at the thermostat (located externally on the
HVAC housing). Assuming that the evaporator coil is fully warmed to ambient conditions, the thermostat should be a
closed circuit.
[Note
: The thermostat circuit opens when the evaporator coil surface temperature drops below 32 de-
circuit, replacement is required. Thermostat replacement requires the complete removal and disassembly of the HVAC
housing. When replacing thermostat, take special care to not kink the capillary tube. Also, install the new capillary tube
in the same location as the original.
POSSIBLE CAUSE #3
~ Perceived lack of cooling due to extreme conditions
CORRECTIVE ACTION
~ Note that extremely high humidity can reduce the effectiveness of the evaporator. The
Am-
bient Temperature vs. Relative Humidity Chart
(below) illustrates how very high humidity can raise the louver tem-
peratures. This test is best performed with the doors and windows open, the blower turned to the highest speed and the
AC system fully engaged. Run the engine at 1500 rpm and allow time for the system to stabilize. Measure the dis-
charge air temperature at one of the dash louvers and compare to the
Chart
.
