Air conditioning: Why does my car AC blow hot air when i run it for a while?

Hi Paul,
I drive a VW Golf V 2008. Since I imported it from Japan, the AC system has been working well until recently when it started blowing hot air when I run it for a while. I employed the services of a mobile AC technician to service the system. This guy filled it with the AC system gas and said it would work well. To my dismay, the situation only got worse. What do you advise me to do?
Gerald.

Hello Gerald, your car Air conditioning (AC) failure looks like a typical situation of AC refrigerant coolant gas is low and needs to recharge or refill. However it is important to take note of two issues about recharging AC refrigerant gas. Under filling the AC refrigerant will prevent the AC system from working normally, on the other hand overfilling the AC refrigerant is just as bad.
There are two possible explanations why your VW’s AC system may have failed despite the recent AC refrigerant recharge. It may have been overfilled, especially if the AC technician did not use an AC recharging system with a pressure gauge to monitor the gas pressure as you fill up.
The second possibility is an AC refill before fixing leakages or carrying out a diagnosis for broken down components such as the AC pump heat exchanger or drier filter.
An AC repair or service centre will be able to diagnose the trouble spot. Always remember to check if the AC refrigerant used to recharge your AC system is the recommended R 134a. The specification of AC refrigerant or coolant should be adhered to because it plays a crucial role in the maintenance of the AC system components by lubricating and preventing corrosion.

Hi Paul, I own a Nissan Xtrail and lately it has developed a screeching noise when I brake. One of the front wheel also makes a humming noise when I drive along. My usual mechanic suggests that I need to cut the discs and replace the hub. Can you provide a second opinion.

Hello Paul, different noises from the wheels, suspension and steering system will suggest a fault. Whilst one can make an informed guess it is always prudent to carry out a road test and physical inspection before drawing conclusions. Screeching or squeaking noises when you brake are often associated with worn out brake pads or discs. Again a physical inspection is mandatory to determine whether the damage is due to normal wear or whether it is premature wear due to use of defective or cheap low quality brake pads. Often the quality of material used when composing the brake pads will determine their performance.
Today the market is flooded with so many alternative brake pads made of different materials such as metallic, organic or ceramic and it can be confusing even to the mechanics.
The genuine brake pads from the Nissan dealers or reputable independent brands, though more expensive, last longer and will not damage your discs during their lifespan. Before skimming the discs on a lathe machine to remove the ridges caused by the worn out or defective brake pads your mechanic should carefully examine the disc width and ensure that he is not going to skim (cut) below the minimum width.
This will affect the brake efficiency and increase braking distance with the risk of the dics cracking when you brake hard. So outright replacement of brake pads and discs may be recommended.
The wheel hub is the central part of the wheel carries the wheel lugs and is a housing for the wheel bearing. This component enables the vehicle wheel to move freely. A failure of the wheel hub bearing can be caused by driving unevenly worn out tyres or poorly aligned wheels for a long time. Damaged wheel hubs usually cause wheel wiggle or humming / grinding noise as you drive.
Your mechanic can tell the extent of damage by lifting the vehicle and checking for excessive sideways movement of the wheel on the hub assembly. Free spinning the tyres will also confirm the noises mentioned above. Outright replacement of the hub bearing is inevitable.

Hi Paul, My Toyota Ipsum 2002 speedometer is not working and the check engine light is showing. The problem started when my automatic gearbox started shifting poorly from time to time. What could be the problem, my mechanic can’t explain what is wrong.
Alex

Hi Alex, the failure of your speedometer, poor auto transmission shift quality and check engine light is more than a sheer coincidence. My hunch is you have a faulty Vehicle Speed Sensor. Most post 1998 vehicle models employ Vehicle Speed Sensors (VSS) which use Hall Effect (magnetism) or gear drive to track transmission or differential rotation and relay the information as vehicle speed.
This information is used by multiple vehicle components such as the transmission computer, engine computer, speedometer and on some newer models the anti lock brake as well as speed sensitive steering systems. Driveability issues on different cars will depend on how many functions rely on information from the VSS. The presence of a check engine light displayed on your dash board means that if you can access a garage with a computer diagnostic tool, a reading should find a diagnostic trouble code which will confirm if the VSS is faulty.

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By Paul Kaganzi (0772316145)