I assume by "disengage" you mean the engine revs drop off back to around 600ish then theres a pause before it starts pick up to the revs for when the air con cuts in. There is a sensor actually on the aircon compressor but it would be a bit of a trial and error swap to find the fault as i don't know the aircon circuit.
If you look here theres a few diagrams may give you some clues http://www.toyodiy.com/parts/p_E_1995_LEXU...QFW_8719.2.html
Thanks for the reply, I will try and analyse with help of a friend with a brain. Regards.
Sounds like you got yourself a leak somewhere, the low pressure switch is cutting the power to the compressor clutch to protect it, after a while once the high and low side pressure equalises the switch comes back in and allows operation of the compressor albeit temporarily, NO a/c systems require recharging as a service the refrigerant Never wears out just escapes!
Air in the system??? theyre full of sh*t air in any a/c system is certain death! your system needs pressure testing and a leak test carried out , once you have located the leak and sorted it then you can vac it out and recharge to the correct amount.
Hope this helps,
good luck!