Ok guys, this is the deal. The A/C worked just fine in my Prelude until I pulled the engine and put it back in. Now, when I push the A/C button it does not light up and of course nothing happens...air blows but the compressor never kicks on. I checked all the fuses and they are good. I also ran the car with the A/C button on and manually shorted the pressure switch...nothing. Now when I apply 12 volts to the compressor it engages. Both rad fans come on when the engine gets hot enough. I know I put way too much info here but I wanted to eleminate anything I could.

Any ideas guys?
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Did you recharge the A/C system once the motor was back in?
Or did you not recover the refrigerant when you pulled the motor, not opening the A/C system, [not disconnecting condenser, accumulator, evaporator or compressor] hoping you would not need a recharge?

If you get the compressor going with A/C turned on and supplying power directly to the compressor and you still do not get cold air, there is no refrigerant, [R134a] in the system.94

 

Well, when I shorted out the pressure switch on the condenser, that bypassed the notion that the charge may have been lost. I did not break the A/C system open at all. I dealt with the same thing on my Integra a few years ago when I sprung a leak...I shorted the pressure switch connector and the compressor and both fans came on. That was not the case with the Prelude....I had to add 12V directly to the compressor using a wire. See why I am confused a bit LOL?

Edit: I know the ECU has a bit to do with the control of the AC system but it should have nothing to do with why the light does not come on the A/C button in the dash.....

 

If A/C indicator light is not comming on then it's probably a wiring issue.
Most Honda/Acura A/C switches are 2PST, [2 poles on/off] and close a ground circuit, ground input comes from blower motor speed switch, [blower motor must be on for A/C to work] one pole supplies a ground for the indicator bulb, [LED] and the other supplies a ground to the A/C thermostat, which in turn supplies a ground, [when closed] to the A/C pressure pressure switch, which in turn supplies a ground the the A/C compressor clutch relay, or to the ECU/ECM that in turn sends a ground to the A/C compressor clutch relay that in turn supplies the compressor clutch with 12V+.

So find A/C compressor relay and make sure there is power, [12V+] on both the relays coil, [#85 or #86, hot when ign. switch on] and relays input, [#30 or #87, hot at all times] you can jump #30 and #87 to see if compressor clutch engages, if so, supply a ground to relays coil, [395 or #86, opposite of hot side obviously] to see if relay works, you can even supply a ground to the pressure switch plug, [load side] to see if that will engage the compressor to narrow down where the problem may be, but with the indicator light not comming on makes me think the problem is at the A/C switch or wiring going to it.

You did turn on the blower when testing the A/C, right? 94

 

WOW! Thanks man...I will look into it......I did have the blower on.