Cabin heating issue - 1993 W124 300CE
 

Hi!

I have an issue with my cabin heating.

Here are the symptoms:

- Start up the car on a cold day, drive until the engine warms up a bit
- Turn on the cabin air and set the temp to the mid-70's (should heat up the car)
- Blows cold outside air without heating it up

Here's how I fix it (strange.. but this 'fix' works consistently):
- Sudden acceleration. I'll be sitting at a light, and on green I'll jab the throttle a bit, and suddenly, the air coming out of the vents is warmed up! No kidding, I've tried this on more than a dozen occassions and it works every time. If I don't do this, the air doesn't typically start blowing warm by itself.
- I've tried to see if sudden braking would also be a fix, but it doesn't seem so.

Any thoughts on the problem and a permanent fix??

Thanks!!

There is a pump near the washer bottle that pumps when you are at idle. Does the car have heat when you are driving?

Does it have heat while I am driving? Yes, in the sense that when the engine warms up, and after I've done my 'fix' described above, the cabin hvac will blow warm / hot air.

Id look at that pump, the mono valve, and do a flush while your at it. Those are the only 3 possibilities.

When you punch the throttle, you increase the rpms of the water pump, therefore increasing pressure. Something "breaks free" and starts to let the hot water through.

So when you say "look at the pump", you mean the water pump, or another pump?

It recently had a coolant flush actually following a replacement of a hose (this problem was ongoing before the flush as well).

There is a small electric pump that is mounted near (below slightly) your washer fluid bottle. It supplies hot water to the cabin when the car is at idle when the mechanical water pump does not have enough power (rpm)

Ah, thanks for clarifying! I will check that out soon and post back.