A/C cut out

[Paul64]

I was in the E300D this afternoon in the first of the summer traffic jams and it was around 28C.
All was working fine with the A/C then after a while, the compressor cut out though the ventilation fan was still operating, no problem.
The engine temperature was up around an indicated 105C - is there a cut-out in the A/C circuit to effectively reduce the load on the cooling system when load is high??

Got back in the car again after 3 hours, all fully operational again...

Any thoughts?

Thanks

Paul

 

[andy27168]

Hi,
Do the fans in front of the radiator work? If they don,t the A/C gas pressure will increase vastly reducing the cooling available, if the engine got to 105 I would be looking at these fans and the engine cooling fan for any possible issues.

 

[Paul64]

Hi Andy,

I'll check out the 2 speeds and see what's going on - the temperature never goes over 105, however hot the day or heavy the traffic hence my thoughts of the protective device in the a/c system...

Thanks for the heads up - will report findings at the weekend.


Paul

 

[Paul64]

Certainly, the fans are working on A/C operation and as the temperature never gets over the 105 sitting in traffic with the A/C tripped out, I'm guessing the fan cuts in correctly for the engine temperature too... Perhaps there's more info from a wiring diagram on the net, I shall investigate!

Paul

 

[coalville126]

On my W126 when the engine viscous fan clutch was on the blink, the a/c compressor disengaged when the temperature guage rose above the 100 deg mark even though the electric cooling fan was running.

If I'm not mistaken, when the electric fan cuts in due to high engine temp, it automatically disengages the a/c compressor. I've not experienced it since I fixed the fan clutch.

 

[Paul64]

Well, set to this afternoon - changed the clear pipe seals for Viton as there was a bit of stumbling at idle and a bubble settling at the top of the pipe from the filter block.
That went OK, no worries however, I decided to do a bit of checking on the viscous coupling.
I went out in the car to check the injection system and the engine temp was up to around 85C when I got back.
I decided to leave the engine idling and stop the fan to see what the operation of the coupling worked.
I slowed it to a stop using a broom handle and it was very easy to spin backwards if required.
I held it stationary whilst the temperature rose to around 100C and there seemed little difference to the operation of the fan coupling. If I let it go, it would start to rotate with the engine but it was quite easy to stop again and spin backwards.

Should the fan actually have locked up by this temperature or is there just a bit more drag on the coupling to keep the fan turning??

Paul

 

[coalville126]

It will not be physically locked up if it is viscous coupled and not machanical / magnetic, just extremely stiff to turn once the engine is off and the temp is over 90 degC. On mine when the fan clutch had failed, the fan could be stopped by just grabbing it - not that I suggest you should try it.

I have mentioned this on another thread that the viscous clutches are fixable, if the unit has failed due to oil loss, normally through age. Then again replacements aren't that dear.

Fairly straightforward to disassemble the unit once on the complete fan/coupling is off the car.

Clean up the bi-metallic strip and remove it - just clips on. Then pull out the actuating pin. Oil can be added through that hole with - silicone oil, normally used on model car diffs. I gently heated the unit with a hot air gun to speed up the intake of oil.

Fiddly, but definitely do-able.

 

[Paul64]

Great, thanks - might check out how much a new one is - can't be that bad, spreading the cost over 15 years.....

Paul

 

[ianrandom]

Fan clutch should apparently chop a carrot when the engine is warm. So it sounds like yours is buggered. They are like 300 from MB normally, but EuroCarParts had one for mine a while back for something like £69! Its a good make too, Sachs. Remember your forum discount code and get 25% off too.