WD Catalog 2018

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10-9 Go to o - Index
Solenoid Valve—Located on the HVAC unit or near the water valve.
It receives power from the circuit board and controls the air supply to the
water valve.
Air operated Water Valve—The preferred location is on the engine
side of the firewall. Air pressure to the water valve is controlled by the
opening and closing of the solenoid valve. When the solenoid valve is open,
air pressure closes the water valve. The water valve is located on the inlet
side of the heater core.
You will need Constant Temperature Control analyzers to troubleshoot
the CTC™ systems. The vehicle must be operating at proper engine
coolant temperature, air pressure and voltage output in order to trouble-
shoot the two possible failure modes.
Servicing and Repairing the Heater
Heater service and repair may be necessary because of lack of maintenance.
The rubber parts: belts, heater and radiator hoses all fail in time. Engine
coolant should be replaced every year and the whole system should be flushed
when this is done. The thermostat and radiator pressure cap may fail from
metal fatigue.
Heater valves (water and air), the core, or control devices may malfunction
and require adjustment or replacement. In addition to your normal tool chest
items, the cooling system test equipment required is described in Chapter 6.
Summary
By now you should have a pretty good idea about what is involved in HVAC
function, service and repair. With a sound knowledge and understanding of
fundamentals and typical problem areas, your experience on the job will
quickly add to your ability and confidence. Chapter 11 gives you a better
understanding of where components may be located and how they go together.
A series of photos and exploded view illustrations of the typical air conditioner,
heater and combo systems are described. Before you study them, you might
want to review the photos and drawings in earlier chapters.
HVAC Control System Variations