I don't mean to be negative, but I don't believe that your circuit is adequate.
Generally A/C uses 20amp breakers. That's what I have for my home A/C, which is hard wired. A 40 amp 220 breaker will say 40 amp -- not 20.
My stove circuit has a 40 amp breaker -- and it's labelled 40 amps
Check the wire size in the receptacle -- if your A/C is 20 amp, the wire will probably be 12 gauge.
From your description, the heater will certainly need a 30 amp breaker. -- It could draw 22 - 25 amps. The fan will also draw some -- although nothing too serious.
The pigtails and plugs are also rated for amps. Generally they are rated for
electric dryers and stoves. Dryers are the smaller of the two, I believe.
If you hook up to an underrated circuit with proper breakers, you will blow the breakers on a consistent basis. This will not do your wiring any good.
If your circuit is properly rated, there shouldn't be a problem in plugging in a heater or an A/C. You can only plug one in at a time.
Just trying to help,