300E A/C blows cold then will suddenly blow hot air - PeachParts Mercedes-Benz Forum

WANT '71 280SEL · #1 05-23-2004, 09:27 AM

When driving my dad's 300E, there is a horrible nuissance with it. You will be driving with the A/C on, then the air will just start getting hot. Sometimes if you change the temp wheel it will fix, or it will just fix itself. What do you guys think?
Thanks
David

#2 05-23-2004, 10:40 AM

There is a small grille near the center rear view mirror. Hold some smoke near it and see if the smoke is drawn into this grille while the ignition switch is on.

If not, you need to find the small fan that draws the air sample through that grille. The location of this fan varies within the 124. Mine is in front of and to the right of the glove box. Remove the glove box and see if it's there. If it is not turning with the ignition on replace it.

Good luck,

zafarhayatkhan · #3 05-23-2004, 02:53 PM

Bad conncection for the temp control wheel can result in this problem.

Larry, can a defective mono valve cause this?

#4 05-23-2004, 07:37 PM

The 124 does not have a monovalve. It has a more simple heater control valve. When it fails it fails, it typically does not go intermittent.

Good luck,

richard28 · #5 05-24-2004, 12:07 PM

Someone wrote on a different post that this problem can be caused by a defective auxiliary water pump. BTW, my 88 300ce & 91 300e do have a monovalve in front and to the engine side of the battery.