Compressor HVAC: Description and Operation
General Description V5
Vehicles using the V5 compressor may have differences between installations in the mounting brackets, drive systems, pulleys, connections, and system capacities. Basic overhaul procedures are similar between compressors used on different vehicles.
When servicing the compressor, keep dirt and foreign material from getting on or into the compressor parts and system. Clean tools and a clean work area are important for proper service. The compressor connections and the outside of the compressor should be cleaned before any "on-vehicle" repairs, or before removal of the compressor. The parts must be kept clean at all times and any parts to be reassembled should be cleaned with naphtha, stoddard solvent, kerosene or equivalent solvent and dried with dry air. Use only lint free cloths to wipe parts.
The operations described below are based on bench overhaul with the compressor removed from the car, except as noted. They have been prepared in order of accessibility of the components.
When a compressor is removed from the car for servicing, the amount of PAG Lubricant remaining in the compressor should be drained, measured and recorded. This PAG Lubricant should then be discarded and an equal amount of new PAG Lubricant added to the compressor.
NOTE: Up to 120 ml (4 oz.) of PAG Lubricant can collect in the crankcase. Therefore, it is important when replacing a compressor that the PAG Lubricant in the old compressor crankcase be drained thru the drain plug and measured (discard after recording amount).
All replacement compressors will be shipped with 270 ml (9 oz.) of PAG Lubricant in the crankcase. This lubricant must be drained and retained. Then replace the lubricant in the same amount as previously recorded from the old compressor.
NOTE: Replace only with Isuzu approved PAG Lubricant.
Theory of Operation
The V5 is a variable displacement compressor that can match the automotive air conditioning demand under all conditions without cycling. The basic compressor mechanism is a variable angle wobble-plate with five axially oriented cylinders. The center of control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor that senses compressor suction pressure. The wobble-plate angle and compressor displacement are controlled by the crankcase-suction pressure differential. When the A/C capacity demand is high, the suction pressure will be above the control point; the valve will maintain a bleed from crankcase to Suction: no crankcase-suction pressure differential; and the compressor will have maximum displacement. When the A/C capacity demand is lower and the suction pressure reaches the control point, the valve will bleed discharge gas into the crankcase and close off a passage from the crankcase to the suction plenum. The angle of the wobble-plate is controlled by a force balance on the five pistons. A slight elevation of the crankcase-suction pressure differential creates a total force on the pistons resulting in a movement about the wobble-plate pivot pin that reduces the plate angle.
The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate for lubrication of the wobble-plate bearing. The rotation acts as an oil separator. which removes some of the oil from the crankcase-suction bleed, rerouting it to the crankcase where it can lubricate the compressor mechanism.
General Description HD6/HT6
The HD6/HT6 Automotive Conditioning Compressor and Clutch Assembly is a lightweight, six cylinder axial design consisting of three double ended pistons and weighs 5.8 kg (12.7 lbs.)
Although this compressor is the same for all vehicle applications, there are differences in installations, mounting brackets, pulleys, torque cushions and switches, none of which will affect the following overhaul procedures.
There are two clutch driver designs for these compressors. The clutch driver without a torque cushion and the clutch driver having a thin torque cushion.
Service compressors are supplied with either the control switches assembled in the rear head or a plug may be found where a control switch is required. If the service compressor requires control switches, the plug may be removed from the appropriate rear head switch cavity of the replaced compressor and assembled as prescribed.
When servicing the compressor, keep dirt or foreign material from getting on or into the compressor parts and system. Clean tools and a clean work area are important for proper service. The compressor connections and the outside of the compressor should be cleaned before any "on vehicle" repairs, or before removal of the compressor. The parts must be kept clean at all times and any parts to be reassembled should be cleaned with trichloroethane, naphtha, stoddard solvent, kerosene or equivalent and dried with dry air. When necessary to use a cloth on any part, it should be of a non-lint producing type.
The operations described below are based on bench overhaul with the compressor removed from the vehicle, except as noted. They have been prepared in order of accessibility of the components. When a compressor is removed from the vehicle for servicing, the amount of PAG lubricant remaining in the compressor should be drained, measured and recorded. This PAG lubricant should then be discarded and an equal amount of new PAG lubricant added to the compressor.
The service compressor is shipped with 240 ml (8 oz.) of PAG lubricant. This lubricant should be drained and retained for use as replacement lubricant when service procedures require addition of new lubricant to compressor.
NOTE: Replace only with Isuzu approved PAG lubricant.
Most minor repair procedures may be done on the vehicle without discharging the system. Major repair procedures require that the system be discharged of refrigerant.
METRIC THREAD SIZE INFORMATION
1. Compressor to mounting bracket bolts.
Front M10 x 1.5-6H
Rear M8 x 1.25-6H
2. Suction-discharge port screw.
M10 x 1.5-6H
3. Compressor shaft.
M9 x 1.25-6H
4. Internal hub-clutch drive assembly.
M22 x 1.5-6H