I don't know if this will apply to you but I have a similar problem with my 95 Jetta. What I have noticed are defective contacts on the fan speed selector switch. If the fan is off the a/c cuts out. I have yet to replair the switch (selections 2 and 4 work fine but 1 and 3 cut in and out) but if I tap the switch I notice the a/c will come back in. Hope this helps.
