How does the LS PCM control dual electric fans, and is it enough for an old truck with A/C?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

• The Derale 16749 adjustable fan controller operates one or two fans with a combined maximum continuous draw of 25 amps, has an adjustable turn-on range of 150-240F with turn-off preset 10F below turn-on, includes a ground-circuit relay, a 3/8-inch NPT probe, and an A/C override circuit. (Derale Performance)
• P01/P59; Gen III LS; 1999-2007: PSI stock PCM calibrations turn Fan 1 ON at 226F and OFF at 221F, and Fan 2 ON at 235F and OFF at 230F; when PSI programs the PCM it sets fan-on points to 195F and 205F. (PSI Conversion / Performance Systems Integration (via SlideShare))
• Sources differ: Fan-on temperatures are calibration-dependent: forum-reported custom tunes commonly use 190/205F, and PSI's own reprogram sets 195/205F rather than the stock 226/221 and 235/230.
• LSx/Vortec: Current Performance's heavy-duty dual-fan add-on module uses three sealed relays and two fuses to run two fans in series at half speed first, then full speed; it has 50-amp relays, one 40-amp JCase fuse per fan, 12 AWG fan outputs, an 8 AWG main feed, and ground-triggered control wires meant to interface with PCM fan outputs. (Current Performance Wiring)
• P01 (0411); Vortec truck 4.8/5.3/6.0; 1999-2002: BP Automotive's A/C Update Kit (PN 1018) for 1999-2002 trucks screws into the Schrader valve port and lets the PCM control the electric fans when the A/C is on; it pins three wires into the PCM and requires the PCM to be programmed for fan activation. (Glenn's Auto Performance (BP Automotive reseller))
• Summit MAX EFI 500: The Summit MAX EFI 500's ECU-controlled electric fan wire is a relay trigger only: the ECU grounds the relay trigger at the configured fan-on temperature. (Summit Racing Equipment (via manuals.plus))

Confirm against the instructions for your exact parts before wiring. More: Other wiring in our tuning guide.