A/C System - Manual Correction
91isuzu02
BULLETIN NUMBER SB91-12-003
ISSUE DATE February 21, 1991
GROUP HEATING & A/C
IMPULSE (JI) AND STYLUS (JS) A/C CIRCUIT DIAGRAMS AND TROUBLESHOOTING PROCEDURES (WORKSHOP MANUAL CORRECTION)
AFFECTED VEHICLES
1990-91 Impulse (JI) and Stylus (JS) models equipped with air conditioning.
SERVICE INFORMATION
Some A/C circuit wiring diagrams and troubleshooting procedures are incorrectly printed in the following Workshop Manuals:
Manual Page No.
1991 Stylus (JS) 1B-3, 1B-7,
(Publication No. AIMI-SVC-205, 1B-13,1B-17
part No. 2-90991-052-0) 8-192
1991 Impulse (JI) 1B-3, 1B-7,
(Publication No. AIMI-SVC-204, 1B-9, 1B-15,
part No. 2-90991-062-0) 1B-19, 1B-23,
8-216, 8-220
1990 Impulse (JI) 1B-3, 1B-7,
(Publication No. AIMI-SVC-183, 1B-13, 1B-17,
part No. 2-90990-062-0) 8-180
This Service Bulletin contains corrected A/C circuit wiring diagrams and troubleshooting procedures for the referenced Workshop Manuals.
1990-91 IMPULSE AND STYLUS
The refrigeration cycle includes the following four processes as the refrigerant changes repeatedly from liquid to gas and back to liquid while circulating.
EVAPORATION
The refrigerant is changed from a liquid to a gas inside the evaporator. The refrigerant mist that enters the evaporator vaporizes readily. The liquid refrigerant removes the required quantity of heat (latent heat of vaporization) from the air around the evaporator core cooling fins and rapidly vaporizes. Removing the heat cools the air, which is then radiated from the fins and lowers the temperature of the air inside the vehicle.
The refrigerant liquid sent from the expansion valve and the vaporized refrigerant gas are both present inside the evaporator and the liquid is converted to gas.
With this change from liquid to gas, the pressure inside the evaporator must be kept low enough for vaporization to occur at a lower temperature. Because of that, the vaporized refrigerant is sucked into the compressor.
COMPRESSION
The refrigerant is compressed by the compressor until it is easily liquefied at normal temperature.
The vaporized refrigerant in the evaporator is sucked into the compressor. This action maintains the refrigerant inside the evaporator at a low pressure so that it can easily vaporize, even at low temperatures close to 0~C (32~F).
Also, the refrigerant sucked into the compressor is compressed inside the cylinder to increase the pressure and temperature to values such that the refrigerant can easily liquefy at normal ambient temperatures.
CONDENSATION
The refrigerant inside the condenser is cooled by the outside air and changes from gas to liquid.
The high temperature, high pressure gas coming from the compressor is cooled and liquefied by the condenser with outside air and accumulated in the receiver/dehydrator. The heat radiated to the outside air by the high temperature, high pressure gas in the compressor is called heat of condensation. This is the total quantity of heat (heat of vaporization) the refrigerant removes from the vehicle interior via the evaporator and the work (calculated as the quantity of heat) performed for compression.
EXPANSION
The expansion valve lowers the pressure of the refrigerant liquid so that it can easily vaporize.
The process of lowering the pressure to encourage vaporization before the liquefied refrigerant is sent to the evaporator is called expansion.
In addition, the expansion valve controls the flow rate of the refrigerant liquid while decreasing the pressure. That is, the quantity of refrigerant liquid vaporized inside the evaporator is determined by the quantity of heat which must be removed at a prescribed vaporization temperature and it is important that the quantity of refrigerant be controlled to exactly the right value.
COMPRESSOR
Compressor performs two main functions; It compresses low-pressure and low-temperature refrigerant vapor from the evaporator into high-pressure and high-temperature refrigerant vapor to the condenser. And it pumps refrigerant and refrigerant oil through the A/C system.
The temperature sensor and high pressure valve are mounted on the front head and protect the compressor by stopping it when the discharge temperature and pressure increases abnormally.
MAGNETIC CLUTCH
The compressor is driven by the drive belt from the crank pulley of the engine. If the compressor, however, is activated each time the engine is started, this causes a lot of load to the engine, and is not desirable. The magnetic clutch functions to transmit the power from the engine to the compressor and activate it when the air conditioning is, "ON". Also, it cuts off the power from the engine to the compressor when the air conditioning is "OFF". (Magnetic clutch repair procedure can be found in Section 1D.)
CONDENSER
The condenser assembly in front of the radiator which carry the refrigerant and cooling fins to provide rapid transfer of heat.
Also, it functions to cool and liquefy forcibly high-pressure and high-temperature vapor sent from the compressor by the radiator fan or condenser fan.
A condenser may malfunction in two ways; it may leak, or it may be restricted. A condenser restriction will result in excessive compressor discharge pressure. If a partial restriction is present, the refrigerant expands after passing through the restriction.
Thus, ice or frost may from immediately after the restriction. If air flow through the condenser or radiator is blocked, high discharge pressures will result. During normal condenser operation, the refrigerant outlet line will be slightly cooler than inlet line.
RECEIVER/DEHYDRATOR
The receiver/dehydrator performs four functions;
^ As the quantity of refrigerant circulated varies
1990-91 IMPULSE
WIRING DIAGRAM
LEVER CONTROL TYPE - A/C CONTROL SYSTEM
1991 IMPULSE ONLY
PUSH CONTROL TYPE - A/C CONTROL SYSTEM
1991 IMPULSE ONLY
1990-91 IMPULSE AND STYLUS
1990-91 IMPULSE AND STYLUS
1990-91 IMPULSE AND STYLUS
CIRCUIT DIAGRAM (NON-TURBO MODEL)
1991 IMPULSE ONLY
CIRCUIT DIAGRAM (TURBO MODEL)