AC causes drain on battery

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mjp8877:
Hi. I have a 1971 280sl. Whenever I turn on AC there is a drain on battery and I cant restart the car. The battery is good. The alternator is new (35 amps as recommended in original model). We put in a new voltage regulator but it only got us 1 more amp to work with. The mechanic is recommending a new alternator this time with more amps than was originally on the car. If I dont run AC there is no problem. AC checked out OK. Anyone with any suggestions? Mike

Michael J. Price

al_lieffring:
Michael

Will the car restart if the a/c switch is turned off?


Unlike most cars that had factory installed air conditioning, the Frigking unit that was dealer installed in these cars doesn't have a compressor cut out relay that disconects the power to the compressor clutch when the starter is cranking. Having the compressor engaged adds a lot of extra load onto the starter motor when the A/C is switched on.

I agree with the mechanic too, a 35amp alternator is too small for a car equipped with A/C. I remember the 280s as having a 55 amp alternator, most modern cars have a 85 amp or larger alternator, usualy 100 amps.

Maybee a combination of adding a clutch cut out relay and more chaging capacity is what you will need to get your car starting properly.







Al Lieffring
66 230Sl
Jones'n for a new gas tank

mjp8877:
quote:Originally posted by al_lieffring

Michael

Will the car restart if the a/c switch is turned off?


Unlike most cars that had factory installed air conditioning, the Frigking unit that was dealer installed in these cars doesn't have a compressor cut out relay that disconects the power to the compressor clutch when the starter is cranking. Having the compressor engaged adds a lot of extra load onto the starter motor when the A/C is switched on.

I agree with the mechanic too, a 35amp alternator is too small for a car equipped with A/C. I remember the 280s as having a 55 amp alternator, most modern cars have a 85 amp or larger alternator, usualy 100 amps.

Maybee a combination of adding a clutch cut out relay and more chaging capacity is what you will need to get your car starting properly.







Al Lieffring
66 230Sl
Jones'n for a new gas tank


Michael J. Price

France:
Michael,

Check your switch also; if it's burned out or wonky it could cause your problem too.  I had mine replaced last spring...

Trice
1968 280SL US, signal red/bl leather, auto, kinder seat
Sarasota FL; Alsace France; Switzerland
Think of your Pagoda as a woman with a past...

mjp8877:
When I run car with ac on, then turn off motor I have to jump start battery to get it going, even if I switch ac off. I guess I will go along with mechanic with an alternator with more amps than was on the original car (35 amps)

Michael J. Price

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