CrimsonES3

Hi i have a 1994 lexus es300 this thing is a hell of a car i got it at a great deal but it needed some major tlc... so i have within the last 8 months replace the control arms on both sides, cv axles on both sides, along with the sway bar bushings, slotted and dotted rotors with new breaks.. now under the hood...i have replaced the timing belt, timing belt pully hydralic actuator water pump water by pass hose cam shaft seals crank shaft seals everything to do with the timing, ive also replaced valve cover gaskets spark plugs a few coil packs all of the connectors to plug the coils into.. the radiator the thermostat housing with a new thermostat and i got a sensor that was out of my freinds wrecked 94 lexus that went into the thermostat housing... that was the only used part lol. but i know it worked as i rode in the car before he wreckd it lol. and at first when i got the car the ac was cool ran strong nice and no problems and the temp gauge worked just fine but after all these repairs now the temp gauge wont registar the temp and the ac starts to act up.. every time i turn on the ac it will run for awhile then start to get hot it will blow the coolant out of the hose that comes out of the coolant overflow tank and it pops the cap on the overtank and will spew out of there .. but i can run the car all day long 24/7 with no ac on and no problems at all and it angers me.. not only does my temp gauge stop working for no aparent reason the ac is the real problem its getting into the 100 degre weather and i have a 2 yr old.. the ac blows cold just fine it just overheats the car.. when it turns on it sounds like it strains the car a little bit in the rpms but not to much.. if the ac compressor was going bad would it cause this.. also when i unplug the connector to the sensor on the thermostat housing the fan doesnt increase speed... i had a power steering leak but it was one of the metal lines that ran into the rack it just came loose and we tightend it and never had a problem with it leaking again.. the power steering works just fine... im at wits end with this car lol please please help

ES300doc

First thing to check is that the condenser and radiator are not obstructed with bugs, dirt and debri. If so, you can clean it up with a power washer or head out to the car wash.
If I remember right the cooling fan on the 94 is hydraulic and powered by the power steering pump. The fan should kick up to full speed when you turn the a/c on. Check this by turning the a/c on Max and see if the cooling fan is running at max and pulling air thru the radiator. Same as the engine gets hot, the cooling fan should speed up.

Since you have no reading on the coolant gauge , you likely have a problem with the coolant temp sensor. Check the sensor at the front of the engine, down below the radiator cap.
This has nothing to do with the a/c compressor. The problem lies with getting cool air across the condenser and radiator.

CrimsonES3

do you have a part number for that coolant sensor ill address that asap and ill also go and check the ac out and post a reply