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,


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

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