As Lucid pointed out, there is a delay in the Volvo AC to make sure the engine is up and running before the compressor clutch is signalled to engage. On older models there was a stand-alone delay relay in the system - on newer ones this relay and logic is probably built into the dreaded MCC/ACC circuit board.

Either way, the relay needs to see 12V+ on the line connecting it to the D61 alternator terminal - which is also connected to your instrument cluster warning light. The relay then delays about 8 seconds before operating, and sending power to the compressor clutch. If there is a bad connection or break in the line to the MCC/ACC unit and the relay, the dash light and alternator may work perfectly, but you'll get no AC.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)

Did you perform the diagnostic with the car running? This is the symptom you'd get if you "pulled codes" with key on, engine off. Does the BAT light work correctly? It should be on with the key on, before starting engine, and go off quickly once running.

I'm not familiar with AC codes, but Volvo AC circuits are usually kept inactive until the D+ terminal changes from being a ground (alternator stationary) to 13-14 volts (alternator producing voltage).

This is to prevent trying to engage the compressor before the car is "up and running", in case it was shut off with AC switched on. So yes, I would suspect you may have an alternator (or AC wiring) problem.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.