IIRC it's a fuse like the others on the car, i.e. subject to going intermittent if it's old. However, I can tell you from experience that one of the failure modes involves weak contacts in the ignition switch, which will give intermittent HVAC function without interrupting anything else obvious; I figured it out when I tried jiggling the switch (gently!) when it would occur, and finding that I could restart the blower by doing so. The fix is replacement of the switch portion of the ignition assembly, which does not have to mean replacement of the key lock portion.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)