Q: A/C blows hot on 1 side cold out of other side. Not consistent. ford can't find. on 2002 Ford Thunderbird

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Had car in to dealership twice. Problem doesn't occur while there. Cools fine. Every now & then it starts blowing hot air out of one side while blowing cold out of other side (dual climatrol). Sometimes it will be the right side & sometimes the left. Temperature setting both @ 70. Saw that there have been other similar complaints list on the Internet, (3) but no solutions found. Always happens on a hot, 80+ day.
(2) Answers
Had the same problem with a 2002 TB. Dealer jacked me around to the tune of $1300. They had no idea of the cause and just kept working at my expense.

They finally had to remove dash and fix control valves for the ducts.

Will not know if it is totally fixed until warm weather returns. Good Luck