AC not working

Have a 2000 Ranger 3.0 V6. Back in December I took it to the dealer for oil and water leaks. They replace the pan and timing cover gaskets. That fixed both leaks. The other day I turned on the AC and found that it is not working at all. Started looking around under the hood and found the high side and low side caps for the AC system are off and laying on top of the engine. Could this be the reason why I have no AC??

If the only repair was a pan gasket and timing cover gasket I see no reason why someone would remove the service valve caps at all. There’s no reason to.

Have you had the vehicle in at any time in the past for an A/C check; either at this shop or another? The caps being off should not cause a loss of refrigerant but if a service valve has a slight leak the rubber seal in the cap can help to slow down or stop this leak.
The truck is 9 years old and chances are the system has a leak(s) somewhere. The usual source of the leak is the compressor shaft seal.

The first thing to do is check system pressure to determine if the system is low or out of refrigerant. If good, then fuses, relays, and pressure cut-out switches should be tested.