Get a thermometer and place it in the vent that is blowing cold air. Record the temp after a few minutes. If the temp is approx 15 - 20 degrees cooler than the inside temp of the coach (delta T or temp split) your AC unit is performing at its peak and it will take time to cool down the coach. If the temp difference is less than 15 degrees the AC unit may require service. If it is over 20 degrees look for a blocked/restricted vent.
Ac units will only cool the air approx 15 - 20 degrees based on the inside temp (air going into the cold air return) and not the outside temps.
There is an extensive discussion on the topic in this thread
http://www.thorforums.com/forums/f8/...ture-1700.html
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