Back fan on a/c unit quits blowing when the temp outside gets hot.

What is your question?

The fan on the a/c unit in the back of the van stops blowing when the temperature outside is HOT. The unit works fine when it is run early in the morning. Seems that the unit is overheating when the temp outside is Hot. It blows cold air when it is working. Just does not like the hot weather. The front a/c unit works fine. Thank you for any help you can give me.