I have a 92 mercedes 400e that blow hot air, the freon is full and the blower works.

I assume you are talking about mercedes c300. Is that happening when you set on auto. What happens when you set temperature to lowest settings? When it blows hot, is it hot or warm? Does ac compressor works when you blow hot air? There could be few possibilities: low freon, faulty temperature sensor in the cabin, faulty ac controller, sticky ac/heater door or faulty door motor

Hello Richard...

Looks like fuse #2 feeds your power seat relay.

See schematic for details.
http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1992/400E/SYSTEM%20WIRING%20DIAGRAMS/4292.pdf

If you have climate control it could be the main processor. Something could be shorting the blower relay to keep it on. You would also need to check and see if the system is still full of freon.

Sort of.
If the system is empty, you would need to jumper the low pressure switch to power the ac clutch to put the first can or two of freon in.
Keep in mind the system is supposed to be vacuumed out before adding freon, so if it is full of air you won't be able to put the full amount of gas in.

Make sure your blend door is closing all the way and that the actuator actually works.

Freon is not full. If it goes back and fourth it is pumping then reaching a low pressure on the low side below 35 psi. Pressure while car is off should be pegged. Check at idle should be around 50 psi and 35 psi at 2000 rpms.

Good luck. If problem persists evac system replace dryer and recharge.

Fuse on drivers side strut mount in a tootsie roll sized case. If not blower motor or the regulator underneath it need replaced.

Hi - There may be 2 separate problems. On my 1991 Lincoln Town Car, there is a Thermal Blower Lockout sensor that disables the heater from blowing until the engine temperature reaches a specific temperature. This way if you have vent or floor settings and 90 degrees set and it is winter, you won't get blasted with cold air. When the vehicle warms up, the TBL circuit enables the climate control to blow the hot air. If you use the flr/def instead of the floor or vent control, the TBL should not prevent the heater from working even with a cold engine. On my car, the TBL went bad and always prevented hot air from blowing on the floor and vent settings, even when the engine was hot. Another thing to check is a thermal limitor resistor. It is designed to cut off the blower at very hot temperatures, except if the blower fan is in the hi setting.

As far as the A/C is concerned, can you verify if the clutch is engaging or not? A rapid cycling of the clutch is an indication of low freon. If you are absolutely sure that you are fully charged on freon, I think there are 2 possible causes: (1) Bad pressure switch on the accumulator is indicating low freon that is telling the compressor not to work; (2) a blocked orifice tube.

Your cars use R134. Older cars have to be converted to R134

you may have a leak in your system or the ac condensor could be bad.