i had the air con serviced on my my96 wrx in the summer and it worked a treat..until yesterday,i push the air con button,the light comes on but you can't hear the pump engage,is there anything i should look out for?
cheers

 

is the aux belt attacted still?

Should be a belt from crank pulley to air con compressor..

if it turns out to be air con pump gone I have one for sale...

 

You may have a very slow leak.
THere is more than likely not enough pressure for the clutch to engage in the compressor.
A recharge should sort it.
Also turn on the AC at least once a week to keep it happy.

*****