III-76
Note: A roof mounted condenser or AC unit assembly often includes
a roof mounted receiver-drier (and sight glass) close to the con-
denser.
Heater System Inspection
A heater system inspection is really a combination engine cooling system and heater
inspection. All heater/cooling system rubber parts deteriorate due to the air (ozone),
heat, coolant and oils. They should be replaced at regular intervals to prevent break-
down on the road. Metal parts and gaskets are subject to malfunction or breakdown
due to fatigue and corrosion.
Coolant has a limited life and should be replaced regularly. If it is dirty, the cool-
ing system should be drained and flushed or back flushed (using special equipment)
before refilling with clean water and anti-freeze. Coolant must be hot when using the
hydrometer to check protection (freeze-up) level. The following inspection procedures
are explained in more detail below:
1. Check Heater Control Valve Function
2. Inspect Other Functions
1. Check Heater Control Valve Function
Many air conditioner/heater systems depend on the heater control valve for tem-
perature control and positive closure. You can easily check heater control valve
function as follows.
A. Cool engine – Start with the engine cool, set the temperature to cold and
leave the fan off. As the engine warms up, feel the heater return hose. If the
hose feels warm or hot, the heater control valve is leaking internally. This
type of leak can seriously reduce air conditioning performance.
Performance Inspection
Figure 7-7
These drawings illustrate
conditions you may observe
in the sight glass window.
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