Pressure testing the cooling system on a 190E
 

I've been doing some research on 190E's the past few weeks and it seems like a pressure test is a pretty smart thing to do before purchasing since both the heater core and head gasket are weak points on these cars. What I need to know is if the valve controlling flow to the heater core is similar to the monovalve on the W126's and W123's. If so, I'm assuming that I would have to do the test with the engine running or can I just turn the ignition switch to the second position to get juice to the HVAC system to open that valve up? Is 14 psi what the system should hold? Thanks