Ford Repair: air conditioning, compressor clutch, computer modem

Question
took my 98 merc mystique to get ac recharged, could not get clutch to engage.  system is at 25 psi and has fresh r134-a. what can cause cluth not to engege? compressor spins by hand, so its not seized

Answer
I'm sorry for the delay in getting to answer your question - my computer modem was hit by lightning, and I'm now swamped with email!
Your a/c problem may only be that the pressure of 25 isn't enough to engage the cycling switch (they usually are set about 40psi to turn on, and about 26 to turn off).... if you jumper the switch, it will allow the circuit to be completed without sufficient pressure for testing purposes.
Other possible concerns in the a/c circuit are extensive - there is a relay for the compressor clutch, and a wide-open-throttle relay that the PCM uses to disable the compressor, and a hi-pressure switch that must not be closed -
you'll probably need a schematic from the dealer to follow the paths and determine which item is preventing the compressor to come on.  Ask your local dealer to print you a page from the schematics book (EVTM).
Hope this helps...
Clay