W201 Heater Issues
 

Hello. I am looking for assistance in trying to track down the issues plaguing the heater system of my recently-acquired '91 190e 2.6. So far, I have changed the thermostat and did a coolant system flush and the engine holds good temperature, but the heat remains only slightly warm at best.
In addition, yesterday during my first drive on the highway with this car I realized that the floor vents were blowing completely cold outside air.
Anyone have any advice on what to check or what can be a likely culprit? Thank you!

two things.... you have an aux water pump...and a cylinder looking item that controls heat... both on the passenger side, closer to the firewall..

Bringing this back up as the issue continues.
I swapped the push-button control as I was recommended to do, yet this did not solve the issue. I checked the aux water pump and it seems to be working (you can feel it if you put your hand on it). Additionally, I tried disconnecting the vacuum hose from the heater valve, yet this did not give any better heat output.
So can it be a clogged heater core? Interestingly though, the return hose from the heater core is hot so can that rule that possibility out?
Can it be the water pump somehow not creating enough flow?(However the car doesn't overheat)

The car only blows slightly warm air when at idle and moving below 45mph, but above those speeds the heater gives up.
Any help would be appreciated. Thanks

You may have an air lock from when you did the coolant flush. Check that it may not be your problem, but it could be.

Thank you for your reply. Could you explain how I could see if this is the case/ eliminate it?

Today I tested the heater valve and it is not the cause of this issue. I am now to believe that it is either a clogged heater core, an airlock or somehow faulty/clogged aux water pump (even though it seems to be buzzing and working).