Air Conditioning

The air conditioning uses a refrigerant and various components to cool down the inside of the vehicle. The main components are the compressor, condenser, dryer, expansion valve, evaporator and the blower fan. The compressor compresses the refrigerant making it change into liquid phase. The compressing of the gas causes the liquid's temperature to rise. Then as it goes through the condenser the liquid is cooled down by wind passing through the condenser and removing the heat. The liquid then goes through the dryer where any moisture is taken out. The liquid then goes to the expansion valve where the amount of liquid that flows into the evaporator is controlled. As the Liquid is released by the expansion valve and it goes into the evaporator. The pressure in the evaporator is lower than the pressure in system before the expansion valve. The lower pressure causes the refrigerant to change phase from a liquid to a gas. As the liquid changes to gas the temperature also drops. The temperature of the gas in the evaporator is less than the temperature of the refrigerant gas before it was compressed because heat has been removed from the refrigerant when it was in liquid form by air passing through the condenser. With the evaporator at a low temperature the vehicle can be cooled by the blower blowing air through the evaporator through the vents into the cab of the vehicle.

There are different types of air conditioning compressors, the two that we dis assembled were the piston type and the vane type compressors. The piston type works very similar to an internal combution engine and the vane type is similar to a oil pump or power steering fluid pump. The main reasons why a compressor will fail is that the bearings wear out (due to a lack of lubrication, general wear and tear or a fan belt that is over tightened creating more strain on bearings), the refrigerant leaks out, one of the switches are faulty in the electrical circuit or the compressor clutch is faulty .

Piston Type

Vane Type

When checking the air conditioning on the suzuki we found that the temperature at the vents were not cool enough. We check the compressor to see if the clutch engages when the air conditioning is switched on. we noticed that the compressor does not come on. We thought it may be that the refrigerant was low so we by passed the pressure switch to see if the compressor works. The compressor's clutch would still not engage, this could only mean that the circuit was broken before the pressure switch. We then went to check the fuse to find that it had been removed. Replaced the fuse and the air conditioning works.

Another vehicle had the same problem. The vehicle was a Mercedes Benz c200, the compressor clutch did not engage. We checked for faults using the Hannatech scanning tool. There was a few faults in the air conditioning system and one of them was that the refrigerant was low. We confirmed that the refrigerant was low by checking the current data of the air conditioning system using the diagnostics tool, which showed that the pressure in the system was zero bar. We then connected the manifold guage set to the car and that confirmed that the refrigerant was low.

Manifold guage

Using the same Manifold guage set we created a vacuum in the system using the recovery unit and left it for fifteen minutes to check if the system had any leaks. It is important to check that the system has no leaks otherwise there would be no point recharging the system with refrigerant as it would just leak out. After fifteen minutes the guage was still in the same position indicating that there were no major leaks in the system. We then connected the manifold guage to the scale that was connected to the charging cylinder. If the system is charged on the low pressure side the charging cylinder should be facing upwards so that the system is charged with gas. If the system is charged on the high pressure side the cylinder should be upside down so that he system is charged with liquid. Once the system was charged we closed of the the tap going to the scale/charging cylinder but left the manifold guage connected to the air conditioning system so that we could see if the compressor was working correctly. We started the car, switched the aircon on , put the fan on high, switched the vents to blow out the top and set the temperature to cold. The compressor clutch engaged and the pressure on in the system increased to the correct pressure. The system was cycling correctly and the temperature inside the cabin was correct. We then checked the system again with the diagnostics tool, the current data displayed that the pressure in the system was now 15 bar.

The R134a refrigerant has a die in it that can be seen using a infrared light.
 It used to find leaks in the air con system

screen shot of the Hannatech diagnostics tool after the
refrigerant in the system was recharged notice that the
refrigerant pressure is at 15 Bar not 0 as before

An air conditioning circuit in a car has many safety features/controls to protect the compressor from running without lubrication and ceasing when the refrigerant is low. It also stops ice building up on the air conditioning   system by stoping the compressore when the evaporator temperature goes too low or if the preassure in the system is too high or too low. The safety features/controls switches the compressor on and off to keep the vehicle cool while keeping the system in a safe working order. The switching on and off of the compressor is called cycling.

Suspension strut

The car's suspension strut combines the coil spring and the shock absorber and it also helps control the wheel when the vehicle goes over uneven surfaces. We disassembled a strut to check its serviceability. First we clamped down the spring using spring compressors. NB take extreme care when working with spring compressors, make sure that it is secure before removing the strut top nut. If the spring accidentally releases it may seriously injure someone or result in death. Once the spring has been compressed securely we loosened the the top strut nut and removed the spring and the top mount. We then checked the shock absorber's dampening ability by pushing it in and out. It should go in and out with the same force resisting its movement. We then checked the seal around the struts shaft for any signs of an oil leak. The shaft was also checked for damage and corrosion.

The strut is serviceable, the shock absorber was not leaking oil and it was working correctly. The spring was in good condition. I would recommend replacing the boot as it is torn, a new boot will protect the strut from dust and inprove its lifespand and serviceablity. I also recommend replacing the support bearing as it worn.

Wheel bearings

The wheel bearings are situated inside the wheel hub. The wheel bearings allow the wheels to turn with little friction. The hub usually has two bearings an inner and an outer one. Another crucial part of the wheel assembly is the seals to protect the bearings from dirt and any other foreign matter that may damage the bearings. The bearings are covered with lithium grease for lubricating purposes and because it can handle the heat created by the bearings and the brakes. If there is no grease/little on the bearings it will cause the bearings to create a lot of heat as the wheel turns, the bearings will expand because of this and seize. Once the bearings cool down they may be able to turn again but the will be damaged and will need to be replaced. A damaged wheel bearing can affect the vehicles handling/operation and the passengers' safety.

We pulled a wheel hub apart and cleaned it with brake cleaner. We found that the inner bearing's outer race had marks on it. In this case the hub would be fitted with a new bearing kit (inner bearing, outer bearing, lithium grease and new seals). If one bearing is damaged it is best to get a bearing kit as the other bearing may wear out soon after. When re-assembling the wheel hub it is important that the adjustment nut is not over tightened as this will put a lot of force on the bearings and it can cause them to wear out faster or even cause it to seize. It is also important to make sure that the grease cap and the grease retainer seal properly.

Steering rack

The steering rack is used to convert the steering wheel's rotational motion into a linear motion to change the direction of the wheels. The steering rack uses a rack and pinion gear set to convert the rotational motion it also uses a specific gear ratio to make it easier to turn the steering wheel. The rack also has a piston attached to it with fluid port on both sides of it on the cylinder surrounding the piston. The steering rack has a rotary valve where the steering column connects to the rack, the rotary valve opens and allows high pressure fluid to go to the steering rack piston. The fluid pushes against the piston when the steering wheel is turned to assist the driver when the vehicle is travelling at low speeds.

When servicing a steering rack it is important to fit the rack new seals when assembling it, to prevent the power steering fluid from leaking and to prevent dust and dirt from getting into the moving parts as it will wear it out faster. It is also important to check the play/clearance on the tie rod to rack connection and in the tie rod end ball joints. If there is too much play it may affect the vehicles toe and the vehicle's steering. The vehicle's play on the steering is caused by the clearance between the rack and pinion gears. The play between the gears is adjusted by a bolt that is connected to a nylon yoke, if the bolt is tightened the yoke pushes the rack closer to the pinion gear and when it is loosened the clearance is increased.

 Checking the run out on the rack gear 

Power Steering Pump

The power steering pump is used to assist the driver to steer the vehicle at low speeds. The is powered by the fan belt, it has a similar design as an oil pump. It uses a rotor with vanes on it inside a cam ring to pump the power steering fluid to the steering rack. The pump has a high pressure hose that goes to the steering rack and a low pressure hose that returns the fluid from the steering rack. The pump has a pressure relief valve to let the fluid return to the reservoir when the car is traveling at high speeds.

The main problems that occur in steering pumps is that the fluid lines break or the seals wear out so the pump loses fluid. The bearings also wear out due to its age or the fan belt is over tightened. Most power steering pump pulleys are bolted on to the pump shaft although some are pressed on. To get a pulley off that has been pressed on the pulley needs to be heated up so that it expands and then pulled off with a puller.

Wheel Alignment

Pre-checks

• Jack the car up or lift it up with the hoist. Check the tie rod ends with the wheels on the hoist, have someone sit in the driver seat and turn the steering wheel from left to right vigorously. If a clicking sound is heard when checking the tie rod ends it means they are worn, It could also be checked visually or by feeling it with your hand
• Check the ball joint, bushes and the wheel bearing by raising the vehicle and pushing the wheel from side to side and up and down. If the wheel has play the faulty parts need to be replaced or repaired.
• The tire pressures should be checked and pumped up to the correct pressure

Setting up 

• Make sure that the turn tables are locked
• If the car was raised on the hoist it should be pushed off and back on to reset the suspension joints
• The hoist should be locked into the first pin to make sure that the car is level 
• Once the car is on the hoist and in place the turn table locks should be removed

The car is now ready for the wheel alignment machine

The only thing that could be adjusted on the car that we were working on was the toe because it is a front wheel drive car. Things like the caster, camber, steering axis inclination, included angle etc. Can generally not be adjusted on a front wheel drive vehicle

Adjusting the toe on the tie rod

ABS

Anti-lock braking system. Abs prevents the wheels from locking so that the vehicle slows down faster and so that the driver can control the vehicle while braking hard. ABS uses wheel speed sensors to calculate how fast the wheels are moving and whether they are locked up. If a wheel does lock up the abs system reduces the pressure going to it until it moves the same speed as the other wheels then the pressure is supplied to it again.

The system can be checked with a scanning tool to see if the wheel speed sensors, the motor and the valves  are all working correctly. If there is a problem with one of the sensors a multimeter or an oscilloscope can be used to check the sensor and the wires connecting it to the ABS controller.

Brake booster

The brake booster uses vacuum from the intake manifold to increase the braking force supplied by the driver. The booster consists of a metal canister with a diaphragm, a valve and a rod that goes through it that connects the brake pedal and the master cylinder. When the engine is started the manifold vacuums creates a vacuum inside the booster on one side of the diaphragm. When the pedal is pressed the valve is opened allowing air at atmospheric pressure to enter the booster that pushes on the diaphragm that is connected to the push rod. The push rod pushes the piston in the master cylinder with the force from the driver and the force from the atmospheric pressure/ vacuum from the engine.

The length of the push rod can be adjusted to reduce the clearance between the piston and the push rod. To find out how much the push rod had to be adjusted we measured the length of it from the surface of the booster to the end of the rod. We measured the inside of the master cylinder from the outside edge to the piston and subtracted the distance from the surface that gets bolted to the booster to the outside edge that goes into the booster. We then took the measurement of the length inside the cylinder and subtracted the length of the rod to fined the clearance and how much adjustment the push rod needed. If the clearance is correct the brakes will be more responsive and it could reduce a vehicles stopping distance. 

Brake pipe replacements

If a brake pipe fails (cracks, thread gets strips, damaged) a new one can be made. To make a brake you will need the pipe itself, a cutter, nuts that have the correct thread and a brake pipe flaring tool. Measure the old pipe and cut a piece of the pipe off that is the same length. Check the old pipe to see what type of flaring you need and flare one side of the new pipe then put the nuts on and flare the other side with the same type of flare as the old pipe. Once the pipe has been flared on both sides with the right flare and the bolts are on you can bend it to the shape of the old pipe.

Single flared are generally used when connecting the brake pipes to the wheel cylinders as they have brass inserts that look like olives. Double flares are used on the other end of the brake lines. The brake pipes are flared as another measure to ensure that the connections don't leak.

Bench testing a master cylinder

Once the master cylinder has been serviced/repaired it needs to be tested. We clamped the master cylinder in the bench vice and connected brake lines that have been blocked off. To check if the cylinder was working and if it was holding pressure we filled the reservoir with brake fluid and bled the cylinder to get all the air out. We bled it by pushing the piston in with the brake connectors loosened then closed them and released the piston. We repeated it until all the air was out of the system. Then we pushed the piston in with the cylinder completely blocked off to see if it will hold pressure. If the piston keeps going in it means that the fluid is leaking past the piston seals which means that the cylinder needs to be dismantled to find the problem. If the piston stays fixed it means that the cylinder is fine, the cylinder should be cleaned with brake cleaner if it is not going to be installed in a vehicle immediately.

Caliper repair and servicing

The brake fluid from the master cylinder pushes the caliper piston into the brake pads that push against the rotor to slow the wheel down. The problems that can cause the piston to malfunction is caused by the pistons  seals that are leaking or the piston can rust onto the cylinder. This is why it is important to replace brake fluid regularly and to use the correct brake fluid.

 We had difficulty removing the piston as it was corroded. When it was removed we discovered that the person/s that removed the piston previously had damaged it (damaged caused by hard metal tools). The marks on the piston made it unusable. We cleaned out the caliper cylinder and found that the cylinder had a hole in it. In this case the caliper cylinder and piston will need to be replaced as they are both unrepairable. If they were not damaged the cylinders inside diameter and the pistons outside diameter should be measured to make sure it fits correctly. The pistons seals and the dust seal will also need to be replaced.

 Measuring the pistons outside diameter

Measuring the caliper cylinder's inside diameter

Wheel cylinder repair and service

The wheel cylinder and piston set up pushes the brake shoes into the drum to slow the wheel down. There is three types of drum brake set ups...

 Duplex

Servo

Simplex

The wheel cylinder that we took apart was from a simplex system. It has two pistons in the cylinder facing away from one another. When the fluid from the master cylinder enters the wheel cylinder the fluid pushes both pistons out with the same force unless one of the pistons are jammed or the brake fluid is leaking past the piston seals. If the seals are leaking they will need to be replaced. The wheel cylinder will need to be honed if it is corroded inside (surface rust) if the wheel cylinder is badly damaged it will need to be replaced. NB If the cylinder is made of aluminium it is not possible to hone it. If the cylinder is made from cast iron use kerosene or methylated spirits as a lubricant when honing it. We measured the inside of the cylinder and the diameter of the piston to make sure that the seals will seal properly. Once the cylinder has been honed the we cleaned it with brake cleaner and replaced the pistons after putting rubber grease on the seals to stop them from being damaged. We then replaced the dust seals.

Brake roller test

The brake roller tester is used to measure the braking force of a vehicle. The  machine we used also tested the shock absorbers. First we drove the vehicle onto the shock absorber tester and the machine tests them then we moved the vehicle's front wheels onto the brake roller tester and applied the brakes according to how much the machine specified and once the test are done we applied the brakes hard. Then we tested the back  shock absorbers, the back brakes and the hand brake using the same procedures.

We discovered that the left wheel failed on the park brake test. The vehicle that we tested had inboard brake drums for the park brake so it narrows the problem down to the drums. It could either be the brake shoes, the handbrake cable that is jammed up or the adjustment of the spreader. In our case the shoes still had enough lining on and the cable was not jammed so it is probably the adjustment of the spreader.

If a vehicle with only drums or only rotors was tested and the back brakes are fine but the park brake is not it is more than likely the park brake mechanism that is faulty or the cable is jammed or the cable needs to be adjusted. If there is a problem with brakes it could be caused by air trapped in the brake lines so it will need to be bled or there could be a mechanical fault in the calipers/drums like the piston/s or sliding bolts being jammed and not allowing the fluid pressure to push the brake pads/shoes against the rotors/drums.There may also be a leak in the brake lines or the seals around the pistons, if it there is a leak the fluid will not have enough pressure to push the pistons out which leaves the brakes with a smaller braking force.

 Brake roller tester

 Shock absorber tester

 Inboard drum Park brake

Inboard drum Park brake

Servicing and repairing master cylinders

The master cylinder supplies the brake fluid to the wheel cylinders. The size of the master cylinder is smaller than the wheel cylinder, this causes the master cylinder piston to move more than the wheel cylinder pistons but the wheel cylinder pitons have more force acting on the pads/shoes. Most of the new master cylinders have two pistons, this is mainly for safety reasons. It has two lines that either split front and rear or split diagonally so each piston is connected to two wheels so if one system fails there is another system to slow the car down.

If the master cylinder fails it is probably the seals around the pistons. The pistons need to be removed and the cylinder should be checked for corrosion, because brake fluid draws in water and if the vehicle is parked for too long it can cause the master cylinder to corrode. If it is a steel cylinder it can be honed using methalated spirits or kerosene with a honing tool and then it should be cleaned out with brake cleaner. If the seals have been replaced, the cylinder honed or replaced (if it is aluminuim) and it is assembled it should be bench tested using blocked off fittings to close off the openings for the break lines. The cylinder should hold pressure if it doesn't then there is still a problem with it and it will need to be disassembled again to find the problem. The cylinder should be cleaned with brake cleaner if it will not be installed immediately, otherwise the brake fluid will get contaminated with water and that will cause the cylinder to corrode.

Honing

Secondary piston

Primary piston