1985 W123 300D - AC Problem - HELP!!!

Hello all,
Here is the deal.... I had a bad compressor in my 300D (old one leaked, but still worked), so I changed it. Now, it does not engage.
I have checked/changed/bypassed the low pressure switch, fuse (blower
motor is on the same circuit and operates), changed the push button control unit, verified the system pressure, but nothing. I placed a multi-meter to the compressor wiring and I do not see 12V at the compressor.
I see that there is a AC Comp relay that was used ONLY on the 85 300D and 300SD. I do not have a spare relay to test with. This relay is next to the brake booster (I believe the earlier ones used the small silver "Ice Cube" relay under a panel on the drivers side wheel well.). I do not want to spend $300 and find it is not the problem!
Any ideas???????? It is going to be 90 here this weekend!
Thanks!
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Does the tachometer work on the dash?

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Well if you are well versed in electrical circuit then you can disconnect the wire to the compressor and then connect a live wire from the battery (becareful, dont touch any other part of the body) and short it to the postive (+) terminal on the compressor and hear for a click sound. If you hear the sound then the clutch in air con compressor is okay, if no click sound then it is faulty. If okay then trace for the supply from the relay to the compressor. Hope this help you.
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