Intermittent Heater/AC blower
06-09-2016, 02:03 PM
#1
Junior Member
Thread Starter
Intermittent Heater/AC blower
Hi
I have a 2004 ML500 that has an intermittent heater blower. The symptom is that when I start the car, the blower in the center console ramps up to speed, but about 10% of the time the main blower in the dash area does not start. Sometimes we can be just driving along and the fan will stop. Randomly it may start up again on its own. Changing the speed, switching to defrost and back to AC usually has no effect, but a few times, it did start the fan. It's been happening for about 4 months now, maybe 20K miles or so. Doesn't seem to be getting worse.
I thought I might wait for it to fail completely, then the diagnosis would be simple. But now I'm moving to a place where I will need the AC availability at 100%.
I searched for "blower fan" and got 840 results, and read all that seemed pertinent but there were none for this kind of intermittent activity. The van has 140K miles on it so I'm guessing it could be a dead spot on the rotor of the fan motor if it's a DC motor. But it doesn't act like a dead spot, I've seen that symptom several times before. One of the other posts said the brushes on his motor (I think C class) were completely gone at 140K, so I'm thinking maybe just replace the fan, as it might be needed anyway. But it's quiet, runs well when it runs (most of the time).
One of the other posts said that his blower would run when he shut the speed to 0 before shutting off the car. I think I will try that just to see what happens.
On one occasion, the fan stopped simultaneously when going over a bump. But only one time ever. Could be coincidence. Could be an open ground lead, and I read on a post for a different car that the ground comes through a 3-pin fan connector, not through the chassis. I'm not sure on the ML, so a little info from someone who knows could help.
Any ideas?
I have a 2004 ML500 that has an intermittent heater blower. The symptom is that when I start the car, the blower in the center console ramps up to speed, but about 10% of the time the main blower in the dash area does not start. Sometimes we can be just driving along and the fan will stop. Randomly it may start up again on its own. Changing the speed, switching to defrost and back to AC usually has no effect, but a few times, it did start the fan. It's been happening for about 4 months now, maybe 20K miles or so. Doesn't seem to be getting worse.
I thought I might wait for it to fail completely, then the diagnosis would be simple. But now I'm moving to a place where I will need the AC availability at 100%.
I searched for "blower fan" and got 840 results, and read all that seemed pertinent but there were none for this kind of intermittent activity. The van has 140K miles on it so I'm guessing it could be a dead spot on the rotor of the fan motor if it's a DC motor. But it doesn't act like a dead spot, I've seen that symptom several times before. One of the other posts said the brushes on his motor (I think C class) were completely gone at 140K, so I'm thinking maybe just replace the fan, as it might be needed anyway. But it's quiet, runs well when it runs (most of the time).
One of the other posts said that his blower would run when he shut the speed to 0 before shutting off the car. I think I will try that just to see what happens.
On one occasion, the fan stopped simultaneously when going over a bump. But only one time ever. Could be coincidence. Could be an open ground lead, and I read on a post for a different car that the ground comes through a 3-pin fan connector, not through the chassis. I'm not sure on the ML, so a little info from someone who knows could help.
Any ideas?
06-09-2016, 02:39 PM
#2
Out Of Control!!
Sounds like you have a faulty blower motor preresistor----simply access the fan
from under the IC remove the connector and remove the resistor--bla bla
from under the IC remove the connector and remove the resistor--bla bla
06-10-2016, 12:06 AM
#3
MBWorld Fanatic!
The Blower Motor with Blower Resistor has a 4 wire connector has a chassis ground (W29/2).
Check the connector and the ground and if everything is OK, tap the resistor with a screwdriver handle and see if it cuts out.
Check the connector and the ground and if everything is OK, tap the resistor with a screwdriver handle and see if it cuts out.
