should my acc fan run when ac is on

[mgyver]

should my acc fan run when my ac is on or just when the engine reaches a certain temp
my fan only runs when the engine reaches a certain temp
i thought it was supposed to kick on when the ac was on also

[AusMBtech]

You auxillery fan should operate when your engine temp rises (usually 105degC) over normal temp or when the a/c condensor pressure rises (causing higher condensor temps) due to low air flow. It' shouldn't run as soon as the A/C is turned on.

Newer cars will turn the engine fan on low when a/c is turned on, usually 10% speed.

[300E24V]

AusMBtech, I noticed u r in Sydney!Are you a DIY or a qualified mechanic?
Do you have your own shop?Let us know because it's hard to find honest mechanics these days especially mercedes ones.
Where are you based at?

[AusMBtech]

I'm still an apprentice but I don't have long to go . I work in a Sydney (Australia) merc dealership.

It may be hard to find honest techs, but it's harder to find a salesman or service advisor who is willing to help you beyond their "normal boundrys", that have a good product knowledge or are willing to tell you when they don't know the answer instead of making something up. I've only ever heard of a few............

[300E24V]

Do you do any work outside the shop or does it all go through the shop?
What area are you in?
You are right! service advisor who is willing to help you beyond their "normal boundrys", that have a good product knowledge or are willing to tell you when they don't know the answer instead of making something up. It sounds like you are 1 of the few :p

[AusMBtech]

I do very little work outside the shop, it really depends on what it is. Some jobs just aren't worth doing at home.

I'm in North Sydney, but I work for G Bros, Mona Vale.

Which version of the 300E do you have? The 104 engine with mechanical or electric fuel injection?

I just had a white 300E 24V with mechanical injection come through work today. I prefer the mechanical injection, I think it's a much cheaper system to maintain/less problems than the electonic 104 injection.

[teky]

Originally Posted by mgyver

should my acc fan run when my ac is on or just when the engine reaches a certain temp
my fan only runs when the engine reaches a certain temp
i thought it was supposed to kick on when the ac was on also

it should run when ac is on

[stevebfl]

Through the years the fans are controlled differently. Basically the fan comes on when the refrigerant pressure gets to about 290psi in the drier. This happens quite fast on summer days, thus the fan always seems to be on when the AC is on. This amount of fan (low speed) is generally enough to also keep the engine cool. The high speed fan comes on (same fan just different circuitry) when engine temp is above 100 varies on different years.

A common problem is the burning out of the ballast resistor that lowers the speed for the low speed function. When this happens only the high speed works if the engine gets that hot.

Another common problem is that a slightly low on refrigerant AC will not produce the high pressure necessary to turn on the fan thus the whole car runs hotter.

[Arthur Dalton]

To add to SB post..
If one jumpers the high side pressure sw at the reciever/drier and the low fan works , than the integrity of the a/c fan circuit has passed the test.. so , the common suspect is now low refrigerant..[ or , in rare case , bad presure sw]
This is an easy test when one does not have gauges to verify charge/high side pressure..
Do not expect an a/c aux fan on a cool day , as ambient temps directly affect high side pressures .. [ie.. high side may never get to pressure cut-in spec of switch when amient temps are low.. cool day defrost position is an example of this condition...a/c working without aux fan being called for]

[teky]

we are talking ac not engine cooling arnt we????

[Arthur Dalton]

Originally Posted by teky

we are talking ac not engine cooling arnt we????

Correct..
Engine aux fan is high fan , coolant temp-thermistor sensed..at 105C