I have a '89 F-350 flatbed, 7.3 diesel engine. I was wondering what the possibilities were to install a/c in this truck, if possible, and what the approximate cost would be??

Hello Dumptrucker...
I've worked on my own A/C units so I know a bit about them. Almost Anything is possible with enough time and money. So let's talk about money.
The a/c system will need:
compressor $200
Evaporater $200
Condensor $100
Hoses you want new $200
Dryer(New)You'll want new $ 50
Brackets $100
Evacuate &
Charge134b $200

We're almost at a thousand dollars...give or take a few hundred for used vs new plus labor to install it... I think I'm low estimating because there's always bits your truck doesn't have and you need...

Here in Denver there is a company called Maxair that does a/c installs. I think the last one we had done through the dealrship was around $1600.