Need to know what model RV you have.
Are you absolutely sure the A/C compressor is really running.....or are you assuming that because of the cold air ??
Several "normal" possibilities exist:
The cold air is just sitting in the ducts and will take a few minutes to be purged.
You have a heat pump....which reverses the A/C to make heat and takes a while to get noticeably warm (will never get really hot).
There is a humidity sensor that runs heat and A/C together on purpose.
Have you let it run for 5 minutes or so to see what happens ??