Well I am narrowing down my a/c problem on 1984 300 TD.
COmpressor clutch comes on when relay pins or jumpered.
Aux fan comes on when switch on receiver/drier is jumpered. Not otherwise.
Swapped out ice cube relays and ccu with known good units.
Compressor comes on itermittently, without apparent reason. Aux fan never comes on unless jumpered.
A/c runs ice cold with compressor clutch jumpered.
Any ideas? What’s left?

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Stage Wizards Lighting and sound designer
1981 SD 328,000
1985 300TD, 266,000
1984 300 TD, 267,000