1989 560SEL USA

I suspect I might have a vacuum leak in my A/C control system. I put a vacuum pump on the red/grey vacuum line (near the brake booster). I'm able to create a vacuum with the pump but the system won't hold the vacuum (back to 0 in about 3-4 seconds). Also, last night I drove the car with the system totally off. I felt some air coming through the front vents.

There are three vacuum lines going through the firewall on my car. Red/gray, orange/gray and tan. The other two hold vacuum. I've figured out that the tan line is for the "economy" guage. Am I correct that the red one is for the A/C control? What's the orange one for, door locks? Am I correct in assuming that they should all hold a vacuum?

Thanks
~Dave