Auxiliary fan question - 300CE - PeachParts Mercedes-Benz Forum

rgnprof · #1 06-27-2009, 11:10 PM

I think I have read every aux fan thread, but I have a slightly different question. My low and high speed fans work and come on appropriately - but what turns off the low speed fans?

It has been hot here and if I turn on the A/C the low speed pressure circuit kicks in pretty quickly - but if I turn the A/C off the fans stay on. If I shut the car off and then just turn the key on, the fans start running again. It is not the high speed - car wasn't close to 105-107 C and fans were clearly running at the low speed.

Any ideas?

ryan

Arthur Dalton · #2 06-28-2009, 10:33 AM

Next time it does it, dissconnect the wires at the drier sw with the pigtail leads.

Report that finding.

Also , it takes a little time for the high side pressure to drop, so give me a time frame.

pawoSD · #3 06-28-2009, 04:08 PM

Are the fans supposed to always run on low speed when using the A/C? I'm not sure if they do on my 300E.....the A/C is cold and it does not run hot though. The electric fans do come on if it was turned off and the temp rose while it sits for a while and you start it back up. They ran on high until it dropped to around 90C then they power down....

rgnprof · #4 07-02-2009, 09:49 PM

Sorry for the delay in replying - I have been busy with some other things. I did some more testing tonight per Arthur's suggestions and when I disconnect the pigtail, the fans turn off. Tonight, after driving around town for a while with the A/C on, the fan ran for at least 30 minutes after turning the A/C off. I let the car run for a while, I left it with key on, I turned it off and then turned key on after a minutes - and the fans kept running (they didn't run while the car was off).

I'm beginning to think this is connected to my other electrical issues - see the following thread:

Weird central door lock problem - '91 300CE

I have been monitoring the voltage put out while driving, idling, etc for a few days now - after having replaced my voltage regulator. It's a little better, but not above 14 volts - except maybe on a cool day with all accessories turned off. My central locks still do not work, and the convenience system works sporadically.

Any help would be appreciated.

ryan

Arthur Dalton · #5 07-03-2009, 01:16 AM

Suspect is the pigtail wire/high side pressure switch...

rgnprof · #6 07-03-2009, 09:30 AM

Can I replace without having to evac the A/C system?

ryan

Arthur Dalton · #7 07-03-2009, 09:57 AM

No..it requires evac , unfortunately........

...but you can put a toggle sw in the cabin and use it when you use the a/c.

Correct remedy is to change the sw., but may guys have a toggle already hooked to that sw anyway for a manual fan circuit over-ride modification [for towing and traffic jambs,] so they get used to it.

Might want to put gauges on the system and an ohm meter across the sw to check it's cut-in/cut-out specs.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1991-Mercedes--Benz-300ce-Climate--Control&yearid=1991%40%401991&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6175%3AMBC%7C1498%3AED%7C10000018%40%40300CE&catid=242213%40%40Climate+Control&subcatid=242240@@A%2FC+Temp%2E+Switch&mode=PA

rgnprof · #8 07-03-2009, 10:04 AM

Thanks - that's what I thought. I will fix it right - but is there a way to make sure the switch is bad before going to the trouble to replace it?

I appreciate the help...
ryan

rgnprof · #9 07-03-2009, 10:08 AM

Also, is this one of those - 'while I'm there' procedures??? Should I replace the drier, or anything else since I have the system opened up?

ryan

Arthur Dalton · #10 07-03-2009, 10:09 AM

I just posted that info..

Unplug the sensor and put an ohm meter across the pigtail to see when the sw opens/closes...then put a gauge on the system High Side and put the a/c ON ..watch the gauge to see if the sw opens/closes to specs

The cut-in is 16 bars, the cut-out is 12 bars ..[ if you have the red sw]..which you should gave on that chassis.

If sw is green , specs are 20 bar and 15 bar ,

rgnprof · #11 07-03-2009, 10:19 AM

Probably a stupid 'electrical' question - but, what ohms specs am I looking for? How will I know - by reading the ohmmeter - that the switch is open or closed?

ryan

Arthur Dalton · #12 07-03-2009, 10:25 AM

Zero Ohms..

You are using the ohm meter to check Continuity [ open/closed contacts in the switch]

..or if your meter has a continuity buzzer setting, use that.

It is a cont test, not an ohm value test.

Or if you have an Analog meter , when you zero it in by bridging the test lead, that is the same reading you will show when the sw is closed , and no reading when it opens.

Google Continuity/Ohm meter

You can also just look for fan to cycle, but unplugged is best b/c you are taking the circuity off the table...and just testing the sw in situ and comparing it to spec cut-in/cut-out....

You may also try tapping the sw when the fan will not turn off with no a/c b/c sometimes they stick in the cut-in mode....

rgnprof · #13 07-03-2009, 10:32 AM

Got it - thanks!

ryan