Weak A/C on long trip

I drove my 2004 Corolla 7 hours Sunday on 95 from North Caroina to Maryland. As the day warmed up, I turned on the a/c. It seemed like it was cooling less and less. By the end of the trip, I had the fan on high, and the a/c on recycle - that’s usually the coolest setting. But it was not quite cold enough. It was only in the low 80s outside. Now when I drive it 25 miles to or from work, it works fine. Is this symptomatic of a leak, or need for a recharge (if cars still need recharging)? Thanks for your advice.

Just offhand, it sounds like the evaporator is freezing up. This could be due to a problem with something like an expansion valve or a slight pressure loss in the system due to a minor leak.

All A/C systems leak a tiny bit and this car is 7 years old. It’s due.
What happens is that when the engine and air compressor are running at higher RPMS the high side pressure will climb and the low side will drop. Sometimes the low side pressure may drop much lower than normal and the evaporator temperature will drop into the mid or low 30s. On a short or moderate hop, no problem. On an extended one the evaporator will turn into a ball of ice.

Checking the pressures would be a good first step. The next time the A/C is acting up you might stop and look underneath the car around the passenger side of the firewall. You should see a condensation drip. If not, turn the A/C off, wait 5 minutes, and then note if water starts dripping out. If it does, the evaporator has been frozen and is now thawing.
Hope that helps.

Thank you, that sounds like a very likely explanation. There was a boatload of water on the garage floor after the car cooled down. At least when I take it in for service now, I won’t have to worry that the a/c is symptom free. They’ll still be able to check for leaks. Thanks a million!