Monaco 2002 Diplomat Service Manual page 255

• Keep open flame away from service area. The discharge of a refrigerant
gas near an open flame can produce a poisonous gas.
NOTE: O-rings used in a 134A system are Hydrogenated
Nitrile Butadiene Rubber (HNBR). These are green in color
and required for the 134A system.
A/C Heater:
The A/C system will also produce heat to warm the air in the dash area.
Much like the refrigeration side of the system, a liquid will be used in the
process. This liquid is the engine coolant. The coolant is passed from the radia-
tor to an electronic water valve. The water valve, when open, will allow the
coolant to flow through the heater core. The heater core is tubing and fins. Air
is drawn into the system by a blower motor through the outside recirculation
door opening. Air is blown through the A/C evaporator core and then through
the heater core. When the temperature control is in the WARM position coolant
flows through the heater core. When the temperature is in the COOL position
coolant flow bypasses the heater core. In either position the air flow is felt at
the discharge vents.
Diagnosis of Electric Water Valve:
Theory of Operation: Monaco models with a center dial temperature control
use a potentiometer at the control head for input of desired temperature. The
water valve which controls the water flow to the heater core is opened and
closed by a stepper motor mounted on the water valve. A control module com-
pares the output voltage from the control to that of the feedback for the stepper
motor of water valve. The control module then drives the motor to within one-
half volt of the control potentiometer voltage.
Functional Test:
• Start and operate the engine until the water reaches normal operating
temperature.
• Set the HVAC temperature control to the full hot position.
• The discharge air outlets should have hot air.
• Rotate the temperature control to full cold position.
• Allow 10 minutes for the temperature to stabilize.
• The discharge air outlets should have cold air.
No Heat:
• Check the blower and air mode operations. Fix or repair prior to
proceeding.
• Verify the engine is reaching normal operating temperature. (Check with
engine manufacturer for proper procedure.)
• Check the inlet hose at the water valve. The hose has hot water at the
valve inlet. The inlet water temperature should be the same as the engine
water temp.
• With the temp control on full hot position, check the outlet hose of the
water valve. The hose should be at engine water temperature.
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Electrical Systems - Chassis
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