AC compressor clutch not working and blowing hot air

I live in Pennsylvania and we been having some real hot muggy days. I turned on my AC in my Quad cab and it just blows out hot and the compressor clutch does not come on. On cool rainy days the AC works okay. On hot sunny days it seems not to work. Yesterday I took my mother-in-law to the store and it was really hot air conditioning did not work. When I got home I took to guarding hose and sprayed cold water on all of the air conditioning stuff under the hood with the truck running and after a minute or so the air conditioning crutch started and the AC was working. What do you think it could be? Thank you for your help, Mike.