A/C not blowing after an hour?

For the last several years, when taking an extended car trip after some time the air stops coming through the vents. You can clearly hear the blower running and if you put your hand up to the vent, you can slightly feel the cold air, but it’s not coming through. This used to happen after about 3 hours of driving, but now it happens after 1 hour.

I have had an actuator replaced which didn’t solve the problem, but the clicking when turning on the A/C stopped! I’ve also had the A/C checked several times and each time all checks out okay. They tell me they can’t fix what’s not broken. Recently they checked it again and said it was low on coolant, which is the first time that has happened, but I still have the issue.

I have figured out when it happens, I keep the blower on and turn off the A/C and after 5 minutes turn it back on and it blows through the vents again.

What’s the problem? Two different mechanics charge me to check it and can’t fix it. Help!

Colleen