K 1500 Truck 4WD V8-4.8L VIN V (1999)
Refrigerant: Description and Operation
Accumulator
The sealed accumulator assembly connects to the evaporator outlet pipe. The sealed accumulator assembly functions as a liquid/vapor separator that
receives the following:
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The refrigerant vapor
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Some liquid refrigerant
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The refrigerant oil from the evaporator
The sealed accumulator assembly only allows the refrigerant vapor and the refrigerant oil to flow to the compressor.
At the bottom of the accumulator is a desiccant that acts as a drying agent for the moisture that may enter the system. An oil bleed hole, located near the
bottom of the accumulator outlet pipe, provides an oil return path to the compressor.
A low-side pressure service fitting is on the accumulator. A similar service fitting is provided for mounting the cycling pressure switch. Do not discharge
the system when replacing the switch. Service the accumulator only as a replacement assembly.
Compressor
The Harrison HU-6 compressor is belt-driven by the engine crankshaft through the compressor clutch pulley. The compressor pulley rotates freely,
without turning the compressor shaft, until an electromagnetic clutch coil energizes. When the applied voltage energizes the clutch coil, a clutch plate
and hub assembly move rearward toward the compressor clutch pulley. The magnetic force locks the clutch plate and the compressor clutch pulley
together as 1 unit in order to drive the compressor shaft.
All the replacement compressors from the service parts have 120 ml (4 fl oz) of oil in the crankcase. When replacing the compressors, drain the oil from
the old compressor into an approved container. Note the amount drained. Drain the oil from the new compressor. Fill the new compressor with new oil in
the same amount that you drained from the old compressor.
Condenser
The condenser assembly in front of the radiator consists of coils that carry the refrigerant, and cooling fins, that provide the rapid transfer of heat. Air
passing through the condenser cools the high-pressure refrigerant vapor, causing condensation.
Evaporator
The evaporator cools and dehumidifies the air before the air enters the vehicle. High pressure liquid refrigerant flows through the orifice tube into the
low pressure area of the evaporator. The heat in the air passing through the evaporator core is lost to the cooler surface of the core, thereby cooling the
air. When the process of heat loss from the air to the evaporator core surface takes place, any moisture in the air condenses on the outside surface of the
evaporator core. This condensed moisture drains as water.
Expansion (Orifice) Tube
The plastic expansion tube, with the mesh screen, and the orifice is in the condenser outlet pipe. Refer to Expansion (Orifice) Tube Replacement or
HVAC Component Views. See: Expansion Block/Orifice Tube/Service and Repair
The orifice tube provides a restriction to the high-pressure liquid refrigerant in the liquid line. This meters the flow of the refrigerant to the evaporator as
a low-pressure liquid. The filter screens on both the inlet and the outlet sides protect the expansion tube and the orifice from contamination. Service the
tube only as a replacement assembly.
When the engine is turned OFF with the air conditioning operating, the refrigerant in the system flows from the high-pressure side of the expansion tube
orifice to the low-pressure side until the pressure equalizes. This is detectable as a faint hissing sound for 30-60 seconds. The hissing is normal.
When the system diagnostics indicate a restricted expansion tube, replacement of the restricted expansion tube may not be necessary. You may remove
metal chips, flakes, or slivers found on the screen with compressed air. Reuse the expansion tube under the following conditions:
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The plastic frame is not broken
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The expansion tube is not damaged or plugged
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The screen material is not torn
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The screen is not plugged with fine gritty material
Heater Core
In any air conditioning mode, the heater core heats the cool, dehumidified air in order to achieve the desired temperature. The position of the control
assembly temperature rotary knob determines how much heat is added to the incoming air.
High Pressure Relief Valve
The compressor has a pressure relief valve as a safety factor. Under certain conditions, the refrigerant on the discharge side may exceed the designed
operating pressure. Exceeding this pressure limit may cause refrigerant loss out of the pressure relief valve. In order to prevent refrigerant loss or
compressor damage, the high pressure cutoff switch opens automatically at approximately 3036 kPa (440 psi). Opening the switch interrupts the current
to the compressor clutch. Any condition that causes the opening of the switch keeps the compressor from operating.
CAUTION: Avoid breathing A/C Refrigerant-134a and lubricant vapor and mist. Exposure may irritate eyes, nose, and throat. To remove
R-134a from the A/C system, use service equipment certified to meet the requirements of SAE J2210 (R-134a recycling equipment). If
accidental system discharge occurs, ventilate the work area before resuming service. Additional health and safety information may be obtained
