TORQUE SHOP #4
This issue’s Q&A article is about automotive air-conditioning.
Several car workshops offer air-conditioner gas top-up service. Is it necessary to top up air-con gas? I thought the system is a closed loop and the gas level will not fall unless there is a leak?
You are right about refrigerant in the car’s air-conditioner being in a closed-loop system. This, incidentally, applies to any air-conditioner, even the ones in your homes.
So the air-con gas top-up service is a load of hogwash and a waste of your money. If the car’s air-con is no longer blowing cool air or has begun to perform inadequately in very warm weather, a refrigerant top-up is unlikely to solve the problem.
A low refrigerant level means there is a leak in the air-conditioning system and this needs to be fixed first.
Of course, a top-up will give you some relief, but the fresh refrigerant will soon leak.
While on this topic, it is important to bear in mind that periodic servicing of the air-con system in your car (as in your home, for that matter) is necessary to maintain performance.
This includes flushing and evacuating the system of the existing refrigerant, cleaning or replacing the filters and then recharging with fresh refrigerant. For the car, such a service is not required annually, but do consider doing this for every 60,000 kilometres.
Just stay away from the air-con gas top-up providers.
I was told by a friend, who is an airline pilot, that switching off my car’s air-conditioner is part of the correct shutdown procedure. Is this true?
Certain specific steps are necessary when shutting down an aircraft. As you can imagine, a car is a very different machine. Apart from parking the vehicle in a proper place, shifting the gear lever to P (in the case of an automatic transmission) or first gear (in the case of a manual transmission) and pulling up the parking brake, there is really no other procedure to perform. With most cars these days, the air-conditioning system,
THE AIR-CON GAS TOP-UP SERVICE IS A WASTE OF YOUR MONEY.
even if its switch is in the “on” position, will be activated only when the engine has started and is at least at idling speed.
Not turning off the car’s air-con when shutting down the engine will not cause any electrical or mechanical damage.
Only with old cars – mainly those more than 20 years in age – is the compressor activated the moment the ignition is switched on. This causes additional load to be placed on the starter-motor, which is why it is advisable to keep the air-conditioning off when starting the old car in question.
I have heard that you should switch off the car airconditioner before turning off the ignition. Is this a myth or is there a sound technical reason for doing so?
During the 1970s, when most automotive air-conditioners were retro-fitted accessories, the average family car suffered 10 to 15 percent loss in power.
With these units, it was helpful to have the airconditioner turned off when the engine was shut down, so that the starter-motor had less of a strain the next time the car was started.
So if you run a classic car, do remember to ensure that the air-conditioner is switched off before starting up the engine. Otherwise, the air-conditioner compressor load puts a strain on the starter-motor and battery.
With all modern cars that are fuel-injected and fitted with electronic engine management, this routine is not necessary. This is because the compressor is not engaged – and thus does not impose a load – until the engine has reached its normal idling speed.
Also, the higher efficiency of the air-conditioning system and the engine of modern cars means that performance and fuel economy losses are not as drastic as they used to be.
Your car’s air-con system requires periodic servicing to maintain its cooling performance, like the airconditioners in your home. APRIL 2018