W124: A/C gets tired and engine gets hot. - Page 2 - PeachParts Mercedes-Benz Forum

73Elsinore · #16 07-24-2009, 07:08 PM

In regard to your first question, I once had a Ford Bronco II that would do exactly that same thing. The A/C would work fine for 3-4 hours and then would gradually stop blowing air, even with blower running full speed on max. The cause turned out to be the evaporator was freezing up, i.e. the coils on the outside were getting blocked with ice and that would prevent air from blowing through the coils. The cure was to turn off the A/C for about 10 minutes to thaw out the evap and then it would work fine again for another 3-4 hours. This only happened on long road trips. The evap drain tube was wide open, so that wasn't the problem. I never had it checked out and I just lived with it since the car did it from brand new.

juribe2 · #17 07-24-2009, 07:46 PM

Quote:

Originally Posted by Arthur Dalton

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............

Great! I'll give it a try. I feel so stupid asking but... what size resistor? All I know about resistors is that they have some colour lines that mean the Ohms and tolerance?

Since I'm traveling to USA in a couple of days, I think I'll buy the fan clutch there (MB parts are about 3 to 5 times more expensive here!). In the meantime, I think hacking the system to turn the high fans at about 95-100 would be great.

juribe2 · #18 07-24-2009, 07:48 PM

Quote:

Originally Posted by 73Elsinore

In regard to your first question, I once had a Ford Bronco II that would do exactly that same thing. The A/C would work fine for 3-4 hours and then would gradually stop blowing air, even with blower running full speed on max. The cause turned out to be the evaporator was freezing up, i.e. the coils on the outside were getting blocked with ice and that would prevent air from blowing through the coils. The cure was to turn off the A/C for about 10 minutes to thaw out the evap and then it would work fine again for another 3-4 hours. This only happened on long road trips. The evap drain tube was wide open, so that wasn't the problem. I never had it checked out and I just lived with it since the car did it from brand new.

I don't know if that's the case but sounds logical to me. Compared to other brand cars, my MB always leave a huge amount of water (condensation) on the parking lots floor. I'll keep that in mind. Thanks.

compress ignite · #19 07-24-2009, 07:50 PM

juribe2,

For $10.00 USD you can pick this up at HF in Orlando
(Will your customs let you bring it in,in the baggage?)

juribe2 · #20 07-24-2009, 08:00 PM

Quote:

Originally Posted by compress ignite

juribe2,

For $10.00 USD you can pick this up at HF in Orlando
(Will your customs let you bring it in,in the baggage?)

Wow, this forum is great! thanks for the info. I don't know how to use that tool but I will defently go to HF and take a loot at it and maybe some other interesting stuff.

compress ignite · #21 07-24-2009, 08:01 PM

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=1.10KXBK-ND

juribe2 · #22 07-24-2009, 08:07 PM

Quote:

Originally Posted by compress ignite

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=1.10KXBK-ND

Great !! Thanks again !!

Arthur Dalton · #23 07-24-2009, 08:15 PM

Between 1400 to 1700 on your chassis.
The higher the resistor, the higher the cut-in..but still lower than stock

I like to stay on the upper end to save fan draw and wear, but some guys go as low as 1100 ..NOT my recommend for your car/chassis..V8 cars use the lower cut-in b/c they run hotter. If you are running under 100C , you do not need a high fan . But waiting til 107 is a bit much, so anywhere close to 100C cut-in will give you adequate airflow when needed and a cut-off about 95/96. That is perfect for 104 HFM/SFI system.

Buy different ones and experiment.
And be aware that as you lower the cut-in , you are also lowering the cut-out..so you want to watch both when choosing.- these fans are not continuous run rated. They are AUX only , and should be used as such.

mak · #24 07-24-2009, 09:50 PM

A very useful mod indeed !
can it be carried out on the 103 engine too .value of resistor required ?
mak

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............[/QUOTE]

Arthur Dalton · #25 07-25-2009, 08:17 AM

mak
>

It can be used on any of the systems that use a Thermistor type CTS..The early 103 engines cars did not use thermistor, so they can not use this technique. You can tell on 103 cars b/c the sensor will be the 2 wire blu one. That is the applicable one. Here is the thermistor type sensor needed for mod.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1990-Mercedes--Benz-300e--Base-Climate--Control&yearid=1990%40%401990&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6194%3AMBC%7C1507%3AED%7C10000013%3ASM%7C20%3AEB%7C613%40%40300E+Base&catid=242213%40%40Climate+Control&subcatid=242256@@A%2FC+ACC+Temp+Sensor&mode=PA

If your chassis has that one , then you can do it. [ or the later 4 prong]

Go to Jim F site . He has taken this mod and made a connector that plugs right between the sensor and the connector and sells them.
And his menu has the info for both the early 2 wire and later 4.
Or, just get a film resistor and solder it across the connector plug.
You want a temp tolerant one, not carbon.
Seems like the new forums guys are not aware of this, but it is an old news around here ...just search 'Cool Harness' and there is tons of info from a few years ago.

A Note:

By adding this R across the thermistor/sensor , you do loose the default function of high fan if sensor fails b/c the CP does not see an open circuit b/c of the added parellel resistor...but that no big deal.
And yo do not want to go too low a cut-in b/c not only will the fans run all the time, but that same sensor is also the high temp cut-out for the compressor..I have seen ones that cut the comp off at high themal load before needed b/c the mod fooled the CP too much.
my recommend is anywhere near 100C cut-in for 104HFM. That shaves off 7C and seems to work fine w/o burdening the electrical system, etc...if that does not do the trick, you have something else wrong..like a bad viscous, thermo, or dirty condenser...etc...and covering that up by running the high aux fan at low cut-in temp is not the answer.
Benz claim is the 107 is fine, but we have found this mod to work better, and you will notice that the older mechanical Bens aux fan switches are 212F/100C...so .........................

juribe2 · #26 07-25-2009, 09:18 AM

[QUOTE=Arthur Dalton;2254266
Buy different ones and experiment.
.....[/QUOTE]

I will. Thank you very much !

Arthur Dalton · #27 07-25-2009, 09:26 AM

You can also buy a cheap variable resistor [ Radio Shack has what they call trimmer resistors.. with a screw that turns to change the R value.]
Get a 1K one and put it in series with a regualr Ik resitor. That give you RT of 2K to start with. [ you know that the mod can be anywhere between 1.1K and 1.8K , so you covering the entire Mod. range with this set-up..now you can tweak it to your likeing ]

So, if you bridge that 2K across the sensor circuit and get the car to the temp you decide you want high fan to trigger , back off [ drop R value] the variable R of your test rig until the fan cuts-in , that is your R factor.

Now , just take the R rig off and measure that Ohms value..that is the Resistance you want in the permanent resistor for the mod.and that value will trigger fan at the temp you have chosen. [ like I said before , don't make the mistake of going too low...many love to think they have done so well with there low cut-in w/o any regards to the consequences]

I am also an advocate of making sure that the cars temp gauge is Accurate, b/c you are using that for temp reference in all this stuff/experiments
That is the single wire sensor... and if you place a 38ohm resistor in the sensors place [ to ground], the guage should read exactly 100c.
That assures temp accuracy before the fact.............

juribe2 · #28 07-25-2009, 09:42 AM

I'm taking notes of this MB electronics lessons. Great stuff to learn !! You should write an MB DIY Book !

Arthur Dalton · #29 07-25-2009, 09:45 AM

Yeah...Except I am trying to get away from this stuff, not more involved....

Been doin' this kinda stuff way too loooooooooooooooooong..

As one of my fellow Vet -Wrench puts it..

".. by the time you get really good at this stuff, you don't want to do it anymore "

juribe2 · #30 08-31-2009, 01:23 PM

Hi,

I'm back from my vacation trip to Orlando and a business trip to Brasil.

I bought the fan clutch during my vacation trip and installed it to the car. Motor temperature isue is NOW 100% SOLVED. I also bought and replaced the cabin filters. After 14 years, those filters were a little dirty!

I just wanted to thank you all for your help and specially to Arthur Dalton.

Compress Ignite: I went to Harbor Freight in Orlando. I didn't buy the pulley tool because I found info on building a simple tool to block the pulley, but.... I did buy some other stuff I discovered I needed. Great Place ! Thanks.

Thank you !

Juan