E320 94 Aux Fan - Page 2 - PeachParts Mercedes-Benz Forum

Arthur Dalton · #16 03-04-2008, 10:04 PM

< Also the system is not cooling that good as before. What do you think?
>

As I said, I think you may be overcharged.
Accurate low aux. fan pressure switch diagnosis requires high side gauge readings/measures.
And accurate system charge should be done by weight, although gauges and experience will work well.
One can use eyesight and fan activation to get it close , but if you have a bad switch, that technique is out and system pressure readings are the only [ and correct ] way to verify sw cut-in/cut-out specs....

radunegru · #17 03-08-2008, 09:50 PM

I did replace the pressure switch by letting out all freon. How do I charge it now. Do I need a flush of the system ? Should I add oil? Or just buy one of those cans that have everything inside(freon,dye,oil, sealant).
Also how do I look for leaks. I think I am loosing some.

Larry Delor · #18 03-08-2008, 10:40 PM

You can't just recharge it, just like that.

You should have gone somewhere, and had the refrigerant recovered (sucked out, instead of spewed forth into the air that we are all to breathe), then had the switch replaced and then (this is the part you need to have done next): Evacuate the system (put a vacuum on it), and then recharge with the proper amount of refrigerant and oil.

If the system is not able to hold a vacuum, you have a leak. Dyes introduced into the system can help find those.

Bring it to a professional, and do it soon, before something else breaks or seizes or does who-knows-what. Probably have to replace the dryer now too, since you opened the system, and let who-knows-what into it.

Good Luck!

radunegru · #19 03-10-2008, 05:16 PM

I did replace the pigtail sensor and have the system completely evacuated and charged professionally but still does not work. The a/c cools perfect but the first speed on aux fans does not work.
So I have the following new parts in relays (30 amp and 15 amp) new resistor.
The mechanic told me that the only option is the push unit.
What Do you think?

Arthur Dalton · #20 03-10-2008, 05:25 PM

..znd does the low speed work if you jumper the pigtail??????????????
That is the question.

radunegru · #21 03-10-2008, 05:48 PM

Yes it did work on the low speed.

stevebfl · #22 03-10-2008, 06:46 PM

So... if the low speed works when you jump the pig tails then your problem is that you don't have enough pressure to turn the switch on. Unless you are in Aruba right now I wouldn't think you would see the 290psi or so that it takes to turn the fan on. Verify it with a pressure gauge on the high side. A slightly low charge will also cause this. It doesn't take a very capable AC to make cold air when its 75 or lower outside.

Arthur Dalton · #23 03-10-2008, 07:32 PM

In other words , don't expect to see that fan until the a/c system sees a High Thermal Load ..ie, high Ambient temp condition..
In New England and cooler climates , it is possible to see a perfectly running a/c system that never gets a high side pressure command for aux fan b/c the condenser is not exposed to a High Thermal Load one would see in southern climates ....
Aux fan ONLY comes on when the A/c system is being taxed and the high side pressures are reaching exterme/dangerous pressures...and when this condition is met, the pigtail sw it closed, activating the aux fan...the added fans airflow across the condenser keeps the high pressure in Check..
That is the AUX LOW FANS SOLE purpose.

Once again, gauges will tell the tale if these pressure are not being attained for sw cut-in activation..........

Baically, you should see a low fan when A/C is ON full blast, the car is at stand-still and idle, and it is a HOT/HUMID day ..and even then they will cycle On/OFF according to conditions/pressures..
I think much of the confusion is b/c many car just have the fan wired to come On anytime the compressir comes On, but that is not the case with your chassis system. Benz design mandates aux airflow only when required.
Same goes for the HIGH fan circuit.. one constantly sees post here that claim they never see the high fan when the coolant temp is rising...well, they don't see high fan b/c it is sensed to NOT come ON until coolant temps are in excess of 107C..a rare occurance...
** Many of us do not like that spec and use a resistor modification to that sensor to drop that to a littte lower cut-in temp.**

radunegru · #24 03-10-2008, 08:58 PM

Inside the shop was about 65 (Car A/C in full blast) and with the A/C machine connected to the car pressure showed 300pc and the fan still did not kicked in.
T I will try another climate control unit from another w124 tomorrow. I will post the results.

okc329 · #25 03-10-2008, 09:47 PM

use R134 or R12 refrigerant?

radunegru · #26 03-10-2008, 10:27 PM

Is R134a

Arthur Dalton · #27 03-11-2008, 01:11 AM

Quote:

Originally Posted by radunegru

Inside the shop was about 65 (Car A/C in full blast) and with the A/C machine connected to the car pressure showed 300pc and the fan still did not kicked in.
T I will try another climate control unit from another w124 tomorrow. I will post the results.

You are not following what we are telling you..If you can get a fan activation with the switch jumpered, you do not need a Control Unit.

This is aux fan sw S/32 Diagnostic info right from the Benz AC Factory Manual.

Job 83-544:

Connect gauge to high pressure fitting and run engine until the pressure at the gauge reads 22Bar [ that is approx 320PSI] That equates to a cut-in pressure at the S/32 aux fan switch of 20 Bar [290PSI.] If this is not attained , then run the engine at a higher RPM. If this is still not attained, check refrigerant level.

So, as we are telling you , at the garage/gauge reading of 300PSI, you have not reached the trigger for the switch , and I believe it is b/c you do not have a high enough ambient temp ..you state the garage is 65 degrees ...well, that is LOW ambient temp. If that ambient was 90 degrees, you would have a low fan activation b/c the high side would then be about 325psi with the same charge of refrigerant.

Change whatever parts you want.. but I am telling you your problem is that the high side pressure is not reaching S32 sw cut-in spec and I don't think you even have a problem..
If the sw has a cut-in of 290/295 psi and your guy has a 300 psi on the gauge , then he only has approx 280 psi at the sw. And that is too low for trigger. Very close, but No Cigar.......You get 325psi at that gauge and you will see a fan. And a higher ambient will do just that. If the fan still does not work at a higher ambient, THEN you know you are slighly low on refrigerant.
Changing your Control Panel is going to do nothing for increasing the high side pressures to get to switch cut-in spec. for fan activation.

VEGASTECH777 · #28 03-11-2008, 04:52 AM

This is the very reason I always recomend my customers to wait until it actually gets hot outside, then I can properly recharge their system. Here in Las Vegas Nevada USA we will see ambient temps of up to 120*F. When its 100*F outside I can easily pump in freon till the aux fan kicks in then continue to add a little more till I see 320 over 45 @ idle. Measuring the freon exactly to the cpacity specs always seems to work the best. But sometimes adding some freon when its still not that hot outside will result in overfilling when the temps rise to 100*F.

Here when it gets over 105*F I tell the customers to be happy if the system is cooling at all!
Most new cars work great but the older ones suck and sweat.....

radunegru · #29 04-18-2008, 10:00 PM

Guys Please help
Today it was 91F and the low speed of aux fans did not start
What should I do?????
Did check the A/C pressure It was ok ;;;;;;;
Arthur you did not believe me the first time .... how about now

Arthur Dalton · #30 04-18-2008, 10:05 PM

What was the pressure if you checked it?