406 hdi Air con Probs?

Hi, I've had my 406 X Reg a few months now (not climate control). AC
Compressor was not kicking in when fan and AC switch was turned on. Had a
specialist check it. He put a little gas to test compressor, as far as I
remember the compressor then came on but found a leak in the condenser(the
rad looking part at front). The part was changed a few days ago, the system
was fully vacuumed and gassed, checked for leaks and was ok. turned engine
on, fan, then ac switch, compressor did not kick in. The AC guy checked all
fuses and what he called the pressure switch at the bottom of the condenser.
Four wires at the switch, he said he thinks there should be power at two
points but only one had 12v+ when system is on. According to his knowledge
the AC relay should be behind the fuse board under the steering wheel. could
not find it there. Cant hear anything click anywhere when the AC switch is
activated though the light comes on. He said best thing to do is to take it
to an auto electrician who has a diagnostic program for the 406. Can you
help please? If you cant, could you at least tell me where all relays
concerned are located? Info in Haynes is not much use for AC problems
Please help.
Many thanks