1984 300D AC Compressor Delayed Engagement

[79Mercy]

Hey guys so my buddy recently got a real nice 84 300D and while helping repair a few things i ran into something i have not seen before.

When i turn the AC on the blower comes on and all the proper vents open however the compressor isnt on. If you wait 5 min, and sometimes almost 15 min the compressor will kick on.

I have jumped the pressure switch, still won't come on, jumped the ETR under the dash and made no difference, swapped the push button unit and found both do the same thing.

Is its possible its the regulator/amp thing above the glove box? are they are any tests for this system? Also haven't checked the in car temp sensor yet, would that cause this symptom? I haven't ever ran into so much trouble its a pretty simple system, or so i thought. Thanks

79Mercy