Why does my air conditioner blow hot air under load and blows cold when not? on 1992 Dodge Ram Van B350

While driving, the air conditioner blows cold air, but when I go up a hill or step on the gas the fan blows out hot air. Is there a vaccuum leak? If so, how can I find it?

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2 answers
Sounds like a vacuum leak.See if air is switching to defrost when going uphill.If so there is a vacuum problem.
Look under hood vacuum tubing is small plastic and looks almost like a wire.Look around with a light and
check to see if tubing cracked broken unhooked ect.
ck freon level and pressure you may have a restriction causing high pressure at cruize