[timgrishkevich]

Welcome to the latest episode of uncommon problems with my 190e that confuse everybody

My aux fans turn on when engine gets hot every time. Hot day, stop and go traffic, they are roaring when the engine temp is around 100c, quickly bringing the temp down to near 80c.

The issue is that they do not turn on in relation to the air conditioning.
I went to get my AC recharged yesterday at a Mercedes restoration shop and they noticed right away that my fans do not turn on when my AC is turned on full blast. They would only turn on when the engine got hot.

The shop got the system to 350psi and my AC compressor kicked in and worked with no issues. It was not working before this as the system pressure was too low and the low pressure switch was doing its job correctly. The only issue with my AC system is that the fans are supposed to turn on to keep the compressor cool.

The shop recommended that I change out my climate control relay behind the climate control buttons inside of the car while they do some reading on what could be causing this.
In the meantime they told me to only turn on the AC while the car is moving at highway speeds and to turn it off any time I am stopped or not moving very fast.

Does anybody here maybe have an idea on what can be causing this?
They inspected my aux fan relay in the fuse box and saw that it was working, but was very hot, indicating a short in the system somewhere. They swapped the relay with one of theirs and it also got hot very quickly.

 

[timgrishkevich]

Also my car was low on refrigerant because it sat for probably 7 years. The shop did a vacuum test and concluded that there are no leaks.

 

[timgrishkevich]

Found this youtube video and the top comment is talking about the same issue. Guess i'm not the only one!

 

[Dave Kost]

Hi Tim.

The high side pressure of 350psi sounds too high. At 90 degrees F ambient the pressure should be around 250-270 psi.

So, is your AC working at 350 PSI?

Dave

 

[timgrishkevich]

Dave, I do not think the PSI is at issue. They seemed to follow the factory recommended spec when filling the system. I watched them mess with the pressures trying to get my aux fans to turn on to no avail.
Maybe I am wrong though.

 

[Dave Kost]

Tim. I got the gauges back and thanks for the present!

I remember charging my system to 250 PSI @ 90F. , so 350psi seemed excessive to me unless you are at 110 ambient.

Isn't there a temperature switch on the dryer that turns on the aux fan?

 

[dolucasi]

Mine does not turn on immediately but after a little time it starts spinning at low speed. Not dependent on coolant temp but tied to the AC systems condition is seems.
Not sure if this is the expected behavior, or it is a sign there is something wrong.

 

[Dave Kost]

There is a ceramic resistor behind the driver headlight, at least there was on my 2.3. My fan wasn't working because this resistor was cracked. The terminals were very corroded too. Something you may want to check. These AC systems are difficult to diagnose because MB made many changes thru model years. Probably best to get a specific model year wiring diagram.

 

[Josh]

Unless the conditions require it as determined by the pressure sensor and the refrigerant temp sensor on the drier itself, it is not uncommon for the aux fan to remain off when the AC is engaged until the high side pressure sensor in conjunction with the temp sensor kicks the fan on.

It seems to me that you have high-speed fans, but there is no low speed. You can test that ceramic resistor by bridging from the positive lead on the battery to each terminal on the ceramic fuse. One side will be the low speed, one side will be the high speed. Use a decently thick wire if you do this, and beware of sparks. Key is not required to test this. If you get appropriate fan spin on either side, then you can rule out the ceramic fuse. From there you can start looking at any relays or fuses, and of course the sensors on the drier itself.

On some older MBs that only have the pressure switch, you could bridge the wires and have the AUX fan come on as soon as you engage the AC, but it'll be on high speed (not sure if the older cars had a low speed setting, it's possible that the temp sensor is responsible for low speed, and the high pressure sensor responsible for high speed).

I attempted the bridging on my 190, and found that bridging the pressure sensor did nothing, but bridging the temp sensor turned on the aux fan at full speed as soon as I turned the key to "ON", even with the AC and blower motor turned off. I have the manual climate control, so I'm not sure what additional effects that "brain" inside the dash has on any of this.

 

[timgrishkevich]

Dave enjoy the gift!
Alright I got some info here. I'm gonna go bridge some sensors and switches and see if I can get the low speed fan to turn on. That is the setting that I am missing.

My car stays a lot cooler after replacing my fan clutch so I have a feeling my high speed aux fan setting won't be turning on anymore either.