W124: A/C gets tired and engine gets hot. - PeachParts Mercedes-Benz Forum

juribe2 · #1 07-23-2009, 07:55 PM

Hi guys,

I have a 1995 E320 sedan (W124 / M104) with 95,000 km. It is the German version with a 5 speed automatic transmission, no cruise control and no automatic climate control (manual A/C controls).

Recently the car is showing some symptoms and I don’t know if those are related. Let me explain:

Air Conditioning: works fine almost all the time but after driving for 3 to 4 hours continuously, the A/C gets like tired and stops cooling. I can feel and hear the blower working but all I get is a soft warm breeze. If I turn the A/C off for 15 minutes and turn it back on, it works great again for some hours. I must confess I have never replaced the cabin filters (I will soon, I promise) but I don’t think that’s the problem.

Cooling system. In the last 2 years I have replaced: water pump, radiator, thermostat, pressure cap, expansion tank, serpentine belt and every hose in the system. I guess I could say, the car has a brand new cooling system. The car drives cool almost all the time (85 to 90C) on flat terrain, but when driving up a hill with some load or on slow trafic, it gets really hot (110 to 115). Both auxiliary fans are working (with the A/C and when temp is about 100 to 110) and get the temp back to about 90-95C but it stays in 110 if you keep driving up a long hill. I checked the fan clutch and is in good shape. The main fan spins free if I turn the engine on and off when cool and stops almost immediately if I do the same with the engine hot. I know the aux fans are there for a reason but the motor temperature used to be a lot more stable a couple of months ago.

Codes: I keep getting some codes on Pin 8: Code 40, Transmission overload protection switch… and, Code 41, CAN communication from engine control module faulty. Code 40 shows up from time to time but code 41 is always there when I read codes. I don’t know what this means but the car drives really good all the time.

This are a lot of questions and I really appreciate your patience and time. I’m sure I can save a lot of time and money asking to this forum, so thanks in advance for your inputs.

Do you think A/C and engine temperature troubles are related? I read once that some pressure thing in the A/C system has something to do with aux fans or something. I’ve been searching and reading but I haven’t found the solution to my problems.

Thanks again,

Juan

Arthur Dalton · #2 07-23-2009, 08:16 PM

Jumper the 2 leads at the drier sw with the 6" pigtail harness. [ Red one]
Does that get you aux fans?????????

juribe2 · #3 07-23-2009, 09:18 PM

Thanks Arthur,

Do you mean this red sw? Should I jump this with the engine turned off or running? If running, with the AC turned on?

Thanks

juribe2 · #4 07-23-2009, 10:24 PM

Ok. I did the test and this is what I found:

1. Engine running, A/C turned off. I jump the cables on that red sw and low fans start running inmediately.

2. If the drier sw is not jumped and I turn the A/C on, it takes about 30 seconds for the low fans to start running. After turning the AC off, it also takes a couple of seconds to turn the fans off.

3. Enginne running, A/C off. If I disconnect the temp sensor on the thermostat housing, I get the high fans starting inmediately. I know you didn't ask me to do that but I read this in other post and thought it could be interesting for you to know.

4. I also noticed, after turning the engine off, that you can see lots of tiny bubbles thru the drier visor. I guess that means the system is fully charged of refrigerant, right?

Is everything ok so far? What's next?

Thank you.

Arthur Dalton · #5 07-23-2009, 10:47 PM

What is the ambient temps there ???

juribe2 · #6 07-23-2009, 10:53 PM

It's preatty hot here. Usually 90 to 95.

http://www.weather.com/outlook/travel/businesstraveler/tenday/COXX0008?from=36hr_fcst10DayLink_business

Arthur Dalton · #7 07-23-2009, 11:01 PM

I would start by cleaning the condenser and radiator fins w/soap and a garden hose...may even try and seperate them a little at the top cuz lots of debries gets in between the two.

But, with temps like your climate, I would modify the CTS by bridging that coolant temp sensor [ the one you unplugged for high fan] to get the high fan to come on earlier .
It is a common mod we use. [ Archieves.]

You may also want to mod the a/c low fans to high, but I would try the other first.

And lighten up on the a/f ratio mixture for coolant [ more H20, less A/F..]

Your ac fan operation is normal and indicates a good charge of refrigerant . Your viscous fan may be questionable.
Do you have the same problem if you do not use the ac ??

juribe2 · #8 07-23-2009, 11:24 PM

Thanks a lot Arthur for your help. I will study those mods in the archives and try them.

The viscous fan is the only part I haven't replaced related to the cooling system. I'm tempted to buy a new one and replace it but as I mentioned erlier, It seams to work right. I turn the engine on when is cool in the morning and turn it back off inmediately and the fan spins free for some time, but when the enginne is hot and i turn it off, the fan stops almost inmediately (1 or 2 turns before stop, I think). Is there a better test for this?

Arthur, what do you think about codes 40 and 41 on pin 8? Conde 41 is almost permanent in this car. Somthing to worry about? What is the CAN comunication?

Thanks again.

Arthur Dalton · #9 07-24-2009, 09:13 AM

>>I turn the engine on when is cool in the morning and turn it back off inmediately and the fan spins free for some time, but when the enginne is hot and i turn it off, the fan stops almost inmediately (1 or 2 turns before stop, I think). >>

The fan should not free-wheel when turning the engine off , even when cold.
And that is why I asked the last question of the post. If you decide to answer that , and if your answer is a YES, then the viscous is suspect.

juribe2 · #10 07-24-2009, 10:00 AM

Ooops. I mised that last question when I read the post. I don't know the answer. With this temperatures I always use de AC. I'll need to test for that.

Arthur Dalton · #11 07-24-2009, 10:05 AM

Wel, that takes the termal load of the ac out of the equation, so that is why it is a next test.

If it does not heat up as much, also see if that solves the tranny sw problem...the trans is retarding the ign b/c it is seeing heat load that effects pressures.
Clear that code before trying the car w/o ac and se if it returns.

juribe2 · #12 07-24-2009, 03:06 PM

Hi,

I drove the car for about an hour to test what Arthur sugested. Today we have 95F ambient temperature. Driving the car without the ac was a real pain. This are my observations:

1. Driving on light traffic and moderate speed keeps the engine cool (85 to 90C) and that's the same with or without the AC running.

2. With the AC turned OFF y let the car idle (parked) for some minutes and the temperature climbed kind of fast up to 110. The high fans turned on and cooled the engine back to about 88. Driving really sloooooww uphill had the same effect.

3. Turned the AC ON, parked the car and let it idle for some time. The temperature climbed slowly up to about 95 and stayed there. The high fans didn't turn on. Same thing when driving slow uphill. The AC worked very good during this test.

4. Did test No.2 (no AC) again and got the same results.

BTW, before doing the test I had code 41 (CAN comunication...) on pin 8. I deleted the code. After driving the car for 1 hr and doing all test, I got no codes at all. What does CAN mean?

I think that's it. I guess Arthur is right about the viscous fan clutch. I'll drop a new fan clutch asap and see what happens.

Arthur, I couldn't find the articles you mentioned for the fans mod.

I'm still not sure about the AC dying after 3 to 4 hours of continous use. I guess I'll have to monitor that for some time with the new fan clutch and post back if it fails again. Same thing for code 41.

Thank you very much Arthur for you valuable help. This forum is great !

Juan

Arthur Dalton · #13 07-24-2009, 03:23 PM

The can is the wiring between modules. They talk to one another. It can be caused be low voltage or bad connections, etc..there is a test for the CAN element in the HFM module, [ N3/4]. It is pins L and H at the module, they are looking for 115-125 ohms unplugged at the module. I would not worry about that code right now.

My concern would be the 40 code ..that is the one I wanted cleared and see if it came back..do that when you change the viscous. That could be cause by heat load.

You may be able to just do the high fan coolant temp sensor mod to get a jump on the high fan cut-in.
If you still have a/c problems with extreme heat load, then you could do the a/c low to high fan mod.

Start with the coolant temp sensor mod. This is the sensor that you unplugged to get high fan default. I am not sure of that set-up on a manual a/c system, b/c that sensor is for Climate Controlled systems..must be the same if it defaults high fan..is it blu/2 wire?

Search "Cool Harness"
A guy here sells them made up or you can just get a resistor for a buck or two and bridge the blu sensor yourself.
That gets you HIGH fan early [ like 100C vs 107C factory], which seems to keep things in check better in your type of climates.

juribe2 · #14 07-24-2009, 05:57 PM

Thanks again Arthur.

On top of the termostat housing there are 2 sensors. A small one with a single cable and a bigger one with 4 cables. Disconecting the big one turn the high fans on. I'm attaching a picture of the sensor and another of the "manual" AC controls.

I'll do some reading on the fan mods and get the new clutch in a couple of weeks (taking the kids to Orlando for vacation this weekend). I'll post back when I get the fan installed and tested. Oh, and I'll start to read about removing the fan clutch. It looks dificult. I haven't found the way to block the pulley to get the central screw loose.

Thanks. Juan.

Arthur Dalton · #15 07-24-2009, 06:34 PM

OK

The single pin is gauge sensor.
The 4 pin is the later sensor ..it has 2 independent sensors in a single case ..The high fan section is pins 2 [br/yl] and 3 [bu/gy], so that is where you bridge with a resistor for lower high fan cut-in.
All you are doing with the resistor across the sensor is throwing the thermistor inside that sensor out of calibration by adding another resistor accross it..that lowers it/s value at temp and fools the fan input circuit to coming on earlier [ lower cut-in temp]

Works cool and cost almost nothing............