Foton Series Light Bus. Service Manual — part 18

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During vaporization, it absorbs the heat from surrounding air.

Fig.11-11 shows the basic process of a refrigeration

cycle: flow direction, high pressure or low pressure, and the status of refrigerant.

In Fig.11-11, the refrigeration

cycle is divided into two sides, i.e. high pressure and low pressure sides, by the line between compressor and

expansion valve, with the right side being the low pressure side, while the left side being the high pressure side.

Figure 11-11 Refrigeration Cycle

2. Structure & Function

Vehicle air-conditioning system includes compressor, condenser, reservoir dryer, expansion valve, and

evaporator, etc. What’s shown in figure 11-12 is the refrigeration cycle of air conditioning system of BJ6536.

Figure 11-12 Refrigeration Cycle System

Evaporator:

The warm airflow sent from the cab by the fan flows through the radiator fin and tube of the evaporator (See

Figure 11-13), and the low-temperature and low-pressure refrigerant flowing from the expansion valve absorbs

large amount of heat from the warm airflow when it enters the radiator and tube of the evaporator, and thus turns

into refrigerant gas. This process can cool down the warm airflow flowing through the evaporator, and thus lowers

the temperature within the vehicle. When the warm airflow flows through the evaporator, the moisture in it will be

condensed into drips on the radiator, the dust in water and air can be drained out from vehicle through the

discharge outlet.

High Pressure Side

Low Pressure Side

Condenser

Heat radiated outdoors

Evaporator

Indoors heat taken away

Expansion Valve

Compressor

Compressor

Low-Pressure Switch

reservoir dryer

High-Pressure
Valve

Heat Control Switch

Expansion Valve

Evaporator

Cooling Unit

Condenser

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Figure 11-13 Function of Evaporator

Compressor:

Compressor is the major part of air-conditioning system, it inhales and compresses the low temperature and

low pressure refrigerant gas generated by absorbing heat in the evaporator, and then sends it to the condenser after

having risen its pressure and temperature.

Figure 11-14 Swash Plate Compressor

1-Suction Cup; 2-Pulley; 3-Bearing; 4-Coil; 5-Piston; 6- Friction Ball; 7-Slipper; 8-Swash plate Shaft; 9-Central body;

10-Valve Plate; 11-Valve Sheet; 12-Sealing Washer; 13-Front Cylinder Block; 14-Shaft Seal; 15-O-Ring; 16-Rear body; 17-Rear

cover

Condenser:

Condenser is a kind of heat exchanger, it radiates the heat in high temperature and high pressure gas

refrigerant exhausted from the compressor to the outer environment, turning the gas refrigerant into high

temperature and high pressure liquid refrigerant. (See Figure 11-15).

Evaporated Refrigerant

Evaporable Refrigerant

Cool Air

Warm Air Containing Water Vapor

Water Drips

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Figure 11-15 Condenser

Expansion Valve:

Expansion valve is installed on evaporator inlet. Orificing effect of expansion valve makes liquid

refrigerant (from condenser and reservoir dryer) expand suddenly into low pressure moisture steam (after

temperature and pressure drop). The steam enters the evaporator to absorb the air heat inside vechile.

Furthermore, the expansion valve can also automatically adjust the refrigerant flow according to the refrigeration

load so as to control the temperature within the vehicle.

Expansion valve is divided into inner equalizer and outer equalizer types. See figures 11-16 and 11-17.

Fig 11-16 Inner Equilizer Type Expansion Valve

1- Ball Valve; 2-Pinhole; 3- Diaphragm; 4. Capillary Tube; 5-Evaporator; 6-Remote bulb; 7-Spring

Steam being heated up

Liquid

From Compressor

Steam

Liquidation

Liquid being cooled down
To Input Unit

From reservior dryer

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Figure 11-17 Outer Equilizer Type Expansion Valve

Reservior dryer
① R134a refrigerant has a poor water-holding capacity and ice crystal can easily form in expansion valve if

there is moisture in the system. Crystal would restrain the flow of refrigerant. The moisture in the system will also

have chemical effect with the refrigerant, forming the highly corrosive hydrochloric acid that could damage the

steel parts in the system. The reservoir dryer is therefor used to absorb the moisture in the refrigerant. (See Figure

11-18).

② The volume of refrigerant cycling in the refrigeration system varies according to the heat load, the

reservoir dryer contains and supplies neededrefrigerant timely to the cycling system, and compensates the

minor-leakage as well.

③ The filtering devices in the reservoir dryer can clean out impurities and dirt in the system all the time,

preventing them from entering into the refrigerant and blocking the expansion valve.

Figure 11-18 Reservior dryer

3. Refrigeration Cycle Process

The cycling of the refrigerant can be divided into four major processes, namely evaporation, compression,

condensing, and depressurizing. The corresponding devicdes are the evaporator, compressor, condenser, and

expansion valve. See figure 11-19.

Low-Pressure Switch

High-Pressure Valve

Ocular
To Expansion Valve

From Condenser

Filter Screen

Drying Agent

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Figure. 11-19 Four Stages of Refrigerant in recirculation

(1) Compression

Compressor intakes low-pressure (147kPa) and low-temperature (0℃) refrigerating gas after its heat has

been absorbed in evaporator, and compresses the gas into high-pressure (1471kPa) and high-temperature (70~80
℃) gas and sends it into condenser.

(2) Condensation

The high temperature and high pressure refrigerant gas (entering the condenser) exchanges heat with the

environment air. When the temperature of the gas drops to 40~50℃, gas condenses into liquid.

(3) Expansion

High pressure refrigerant liquid flows through the expansion valve. Valve orificing effect makes liquid into

low pressure (147MPa) and low temperature (-5℃) mist.

(4) Evaporation

The orificed low pressure / temperature refrigerant enters the evaporator and evaporates by absorbing the

heat within the vehicle. The temperature of the refrigerant gas in the outlet of the evaporator is about 5℃. (Note:

In the actual cooling circulation, the temperature and pressure of the refrigerant are subject to the outer conditions

such as air temperature and wind speed, etc.) If the compressor keeps running, the aforementioned four processes

will cycle continuously

11.6.2 Check and Maintenance of Air Conditioner

1. Check prior to application season.
① Check whether the surfaces of the condenser and evaporator are clean, cleanse them if there are too many

dusts, then dry them up with compressed air.

② Check whether the performance of all switches and controlling units are reliable.
③ Run the air-conditioning system, then check the remaining volume of refrigerant by looking through

peephole.

2. Check after application season

Check the leakage with a leak detector. Repair any leakage even though the application season is over.

Replenish refrigerant to specified amount.

Check the oil volume in compressor, and replenish when it’s necessary.

Gaseous State

Condenser

Low-Pressure Switch

High-Pressure Valve

Compressor

Evaporator

Expansion Valve

Reserivor dryer

Liquid State

Blower

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Run engine run at a speed higher than idling speed. Check through peephole whether the volume of

refrigerant comply with specification

Routine maintenance of air conditioner

Check the volume of the refrigerant for every two weeks through inspection window. When the

air-conditioner is just turned on, the flow of air bubbles can be seen, but these air bubbles disappear in a short time,

this means the air-conditioner is running properly. If the air bubbles will not disappear, it means refrigerant is

insufficient, and should be replenished. If you splash water onto the condenser, and cannot find any bubbles

through peephole, it means the volume of refrigerant is excessive, and should be discharged to the standard

volume.

Check the tension and conditions of compressor and fan belts every month. Adjust tension if necessary, and

replace cracked belt. When to check belt tension, use the thumb to press the middle point of the belt with the force

of 100N, its deflection should be 8~12mm. Fasteners shall be frequently checked to prevent loosening, the

checking interval should be at each 2000km.

When the air-conditioner is laid for one or a few months, it should be run for several minutes at engine idling

Rpm every week, even in winter. This would ensure proper lubrication on compressor and its seals, so as to keep

A/C in the best technical condition, and prolong A/C service life.

11.6.3 Maintenance & Repair of Air Conditioner

Poor A/C cooling perfomance is mainly due to refrigerant leakage.

1. locate leakage

Popular vehicle A/C refrigerant used today is R134a. It is prone to escape via connectors and oil sealings.

Refrigerant leakage leads to poor or even no cooling.

① check leak trace

During its refrigerating recirculation, A/C needs fluid to lubricate its seal bearing and other moving parts in

compressor. Slight amount of lubricant could enter A/C cooling system along with refrigerant. If leakage happens

in refrigerating recirculation system, there must be lubricant dirt presenting at leaking spot. Therefore, lubricant

dirts on pipeline or connectors indicate there are leak happening there and need to repair.

② Judging leak status of refrigerant through peephole

Start up engine (around 1000rpm) and activate A/C, set A/C temperature switch to COLD and fan switch to

MAX. One can observe how refrigerant is flowing through peephole to determine if there is any leakage in

refrigerating recirculation system

Normal flow of refrigerant:

Refrigerant appears transparent in general, and air from registers is cold. These indicate cooling system

works well.

Insufficient refrigerant:

Bubble is flowing around, and refrigerant turns white. This indicates that cooling result is not good.

No refrigerant

If serious leakage happens, one can see nothing through inspection door. A/C will not work.

In short, oil stain on all connection spots or condenser surface indicate refrigerant leakage has happened there.

Operator should immediately remove leakage and replenish refrigerant and lubricant, preventing further lubricant

leakage from damaged A/C system.

2. Check A/C system operation

Park vehicle in the place with good ventiliation, keep engine running in moderate Rpm, set A/C fan switch to

MAX to recycle interior air.

① Judge A/C’s condition by inspecting temperatures in different locations. Touch AC system parts to check

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surface temperature. In normal condition, low-pressure pipeline is cold and high-pressure pipeline is hot.

High-pressure Pipeline: compressor outlet — condenser — reservoir — expansion valve inlet. Any hot spot

in the pipeline indicates poor heat radiation, while cold or frozen spot indicates restriction..

Low-pressure pipeline: expansion outlet — evaporator — comprssor inlet. Temperature goes from cool to

cold along the pipeline, but there should be no frozen at expansion valve.

There should be obvious temperature difference between high side and low side of compressor. If there is no

evident difference in temperature, it indicates an obvious leaking in air-conditioning system.

② Check and adjust air conditioner belt. Check A/C belt for tension and surface condition, make proper

adjustment or replace when necessary

.

11.6.4 Precautions for A/C Usage and service

The flowing points should be noted during the use and service of A/C system

1. Refrigerant R134a has high potential heat of vaporization, when it contacts skin or eye of a human being,

it will absorb a lot of heat and vaporize, thus frostbite the human body. Watch out this during operation, in the case

of the refrigerant contacts skin, you should wash with a great amount clean cold water, and go to hospital for

treatment.

2. Refrigerant R134a has no color and odor, which is hard to be noticed. When it is exhausted to air, it can

drop the concentration of oxygen in the air to suffocate people. Because refrigerant gas is heavier than air, it

usually sinks down to the bottom of air, service man should not stand in ducts and pits to discharge refrigerant.

The discharging of refrigerant should be conducted in the place with good ventilation.

3. Refrigerant gas R134a will generate toxic phosgene when it contacts lighted fire. Don't conduct any

welding operations or smoke cigarette in service site.

4. Refrigerant R134a can stain the metal surface after mixed with moisture in the air. Hence, when you are

discharging the refrigerant, relevant surfaces of the vehicle body should be covered by a piece of cloth.

5. Refrigerant R134a is soluble with lube oil, lube follows refrigerant R134a to circulate in the system and

spread all over the internal surface of system. So refrigerant must be drained out slowly to prevent lube oil from

being carried off.

6. Pressure of refrigerant R134a increased rapidly along with temperature increased. Therefore, refrigerant

must be placed under the environment with temperature below 40℃.