1992 es 300 lexus heater is blowing cold

Possible warped head. Maybe need to take to mechanic and have machined.

May be your air modulator. Do you hear a clicking sound behind the dashboard?

it must of had work done on the heater because the control valve is hooked up backwards

There are a number of possibilities.
1. If the compressor has a clutch, do you hear it engaging and disengaging?
2. The valve controlling the hot water going to the heater which mixes warm air with the cold air from the evaporator, is not working properly so it si not maintaining proper temperature.
3. THe temperature sensor that senses air temp at the intake to the AC in the cabin is defective.
4. THis is too comlicated to fix yourself, so you need to take it to an AC expert who knows this particular model.

I have 2000 ES300

either low on gas ,or a fault with the flaps?? check the pipes in and out just behind the bulkhead where the ac pipes goe through and their should be a restrictor valve that only allows a small amout of gas through and this causes the cold ,check these pipes ,one should be hot and the other cold ,if when you start up they are correct then nothing then its a faulty restrictor valve ,or the compressor ,if they stay hot and cold then its a problem with the heater controls or the clima computer if it has one ,also check the fan is coming on when the ac is turned on because if its not then its not cooling the gas in the rad and it will shut off the pump ,then it will not cool ,just like you describe

you need a FAN temp control switch or relay or run a toGGl switch

heater control valve

chances are you have climate control. check and make sure your driveside control is on warm air and not cold air.

probably it just needs freon or a new a c compressor

blows hot air all the time even with the ac on???? with the temp gauge on cold???