mkoons

I live in a desert climate, use my air conditioning year round & its always been very reliable but recently developed an issue. When starting up after a stop the blower speed will drop to almost nothing for about 8-10 seconds then
it comes on full blast. This usually only occurs when outside air temp is 90 plus. It sounds like it is linked to manifold vacuum but that doesn't make much sense.

What do you think?

Plutoe

The AC fan speed is controlled by the AC control unit and fan resistor---it senses both the inside and outside temp to establish applicable fan speeds

mkoons

I understand what you are saying but I do not set the A/C on 'AUTO' Stopping or accelerating should not affect the evaporator blower speed. Have not had this issue for 14 yrs of ownership.

cm60k

Did you diagnose the car..?,

you may have bad Evap. temp. sensor, or not enough gas..??,,

also, did you check the condenser fans, if they working or not..???

-;ZAYED;-

Sulaco

I think I have the same issue. It's not that the blower slows down when accelerating, it's that the air gets ducted elsewhere under acceleration. About 8 seconds after I let off the throttle it will redirect the air to the main vents and I feel it blast again.

I agree its vacuum related. I've done no digging, I rarely drive my w202 right now.

mkoons

Sulaco,
I think we are on the same page, I am going to try switching some of the vent positions on & off, they are all vacuum controlled. I had switched it to auto control and back off the other day and I think that improved the issue.
If I find a fix I'll let you know.With these 20yr old cars it's something new all the time.

Sulaco

amen. Big thanks for keeping me in the loop.

mkoons

Sulaco,

Try this, once you are up & running switch the blower speed up to highest setting for 5 seconds, then back to normal 2 or 3 on blower speed, maybe do this twice. It corrected my problem, hopefully for good.

Sulaco

fantastic. I'll try it once I get my starter replaced.

junkyarddawg

The first thing you should do is try to determine if the issue is blower speed control or air distribution. What this means is , do you hear the fan running at speed but no air is coming out of the vents?
If this is the case then you may have an "air distribution" problem and , if memory serves me right, there is a vacuum distribution block under the hood in the right rear module box compartment area. It should be black in color and have several vacuum lines connected to it. The block has a steel ball pressed into one end of it and this is usually where it cracks open and leaks off the vacuum.
This is easy to check without connecting any test equipment to the vehicle.

mkoons

Not sure if we are talking about the same car but on my C43 I do not see anything that resembles a distribution block or anything with vacuum lines attached to it under
the hood.

DRBC43AMG

There is one somewhere as per diagram attached. If I recall it's somewhere behind the glove compartment once you have removed the thing from the dash area.

cm60k

Good one Daniel..,

i remember; i missed that (45) "Green" vacuum line on my previous C280 last year..

-;ZAYED;-

speed43

The link below may or may not help but might help other ac issues in the future. The guy also has the trouble codes written down.