Trying to take advantage of the unwanted extra time on my hands by working on my daughter's 1980 300SD a/c system. It was working flawlessly until my compressor when out. Had a new system installed and it was working great until just before Winter hit. Now, only the defrost button works. Here's what I've done so far:
1. traced each vacuum line coming out of the rubber multi-port and resolved all major leaks (see orange lines);
2. repaired vacuum line feeding the climate control system;
3. tested each blower and compressor master switch, they work.
4. tried to test vacuum at push button switch but could not register any. In picture #2, there are 2 empty ports. I used a plug on one and my finger on the other.

The problem is when everything is connected, I get no vacuum at the test port (pic #3 & 4). But, using my handheld pump connected to test port, I can cycle through each push button - auto low/high/bi-level and each work fine. Blower and compressor kicks on and temperature changes as I move the temp wheel. As soon as I stop manually applying vacuum, the system turns off.

Although I can toggle on/off the compressor using the a/c switch, the compressor did not cycle when adjusting the temp wheel.

I'm at a loss as to what next needs checking. I'm thinking either the rubber multi-port is not sealing, causing a loss of vacuum or the push buttons are leaking. But if that were the case, why was I able to cycle the system using the manual pump?

I'm considering pulling each of the vacuum lines from the multi-port and connecting them directly to the push button circuit.

Based upon what I've described, did I miss something? Am I on the right track?

Don't knock the temporary translucent orange lines. All I had at the time.

Thanks in advance - John

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John V
1979 300D
1980 300SD