A/C control changes from Maximum to floor on 2000 Safari

Noticed this on trip last week when putting load on engine going up grades with cruise control on. Also duplicated it later without cruise on. Vacuum leak?, vacuum switch module or ? What should I expect if I
take it to the dealer?
Jarhead
"We have no government armed with power capable of contending with human passions unbridled by morality and religion...Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other." -John Adams
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sounds like the vacuum reservoir might not be holding or perhaps the check valve is not working.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.