How do I test the condenser fans on my 1999 C230? - PeachParts Mercedes-Benz Forum

DonB · #1 06-25-2006, 08:00 PM

I just replaced the condensing coil on my 1999 C230's a/c system and now the a/c works better, but not great. Air coming out of the vent is just under 70 deg-F. I watched the condenser fans and they never come on, so I did some testing:

- With the car running, a/c turned on, compressor running:
- Removed each fan connector and checked - 0 volts
- Did continuity check on each fan (at the connector) - open circuit on both
- Disconnected wires at high pressure switch - compressor turns off
- Ran wires from battery (in trunk) directly to each fan - nothing happened (but the wires I used were not very good, might have been a bad connection)

Is everything broken, or did I do the tests wrong? What is the right way to test the fans? Thanks everyone, suggestions greatly appreciated,

Don

PS - The pressures are Hi side = 215 ; Low side = 30 (ambient about 75 F)

mbdoc · #2 06-26-2006, 08:33 AM

The 1996 & later cars use an electronic fan module..

ON the W202 chassis c-class that module in mounted to the left outer frame rail behind the LF tire..behind plastic cover.

AS soon as you turn the A/C on OR if the engine reaches 70F the fan SHOULD come on OR more likely than not YOU will over heat the engine!

DonB · #3 06-26-2006, 10:07 PM

Yikes!! The electric fans don't turn on under any condition that I can see. However, the engine temperature doesn't go over normal (80 deg C on the instrument cluster gauge) unless I sit in traffic for a while on a warm day (80 degF or more). Even then, it only goes up a few degrees. I assumed that the mechanical clutch-style fan was cooling the engine.

Is there a way to jumper-out something on the control module to test the fans? Thanks again,

Don

DonB · #4 07-04-2006, 04:31 PM

Anyone? Should I start throwing parts at it? Any suggestions would be greatly appreciated

Thanks,

Don

DonB · #5 07-04-2006, 10:30 PM

Buckwheat, thanks for the reply, but I didn't think the proceedure from JimF applied to my car since I have a different control (see pictures). Is there a way to do the same diagnostics with this one? I tried several button pressing combinations, but none seemed to do anything. I was hoping to get some messages on the instrument displays, but nothing happened.

On the fan test, is 12 Volts-DC from the battery good enough or do I need something with a special waveform? I thought I read something about the fans being variable speed, so if they are, do I need a special test or ???.... Again, any help figuring this out is appreciated,

Don

240dcar · #6 04-30-2013, 11:28 PM

Hi Don & mbdoc, (still wonder How to test) Are the Condenser AUX Fans regular DC motors that 12-14 volts will make spin? See a sticker L76A25 12V---> on fan. Was tricky to unplug or pry loose plug by resistor. My replacements do nothing at 12V, an original is smashed. I see the shroud is a horrible bug & dirt trap. Got plastic off removing pins from expanding pegs. Found it was full to fan opening and into motors with dirt and bugs. A vacuum clean compressed air job to plastic box would make air flow better! - '94 e320 w124 Thanks.

240dcar · #7 05-05-2013, 11:46 PM

A good fan (twin fans both powered) spun by hooking up between 3 and 13 volts DC to the plug at the fan Positive on pin 1 to spin forward other way for backward. Spins fast at 12 VDC and slow at 4 volts (pulling 1.5 amps for each fan). One bad fan started working after squirting water into holes on back of motor and spinning it to sling out the rest of the dead bugs and dirt. A video of the single motor 2-fan with drive belt system seemed to act in a similar way.