don't know it this applies to other vechicles - on my ram the heater core is right next to the a/c condenser. all that hot coolant right next to any a/c components can't help cool things off any especially when the cab temperature is 130+. on my two heater hoses, i installed a 1/2" brass ball valve with 5/8" barb fittings - cutting off the coolant to the cab. the difference is night and day, actually had to turn the a/c down. used to get as cool as 43 after driving a while, now it gets down to 39 within only a few minutes...

 

Makes good sense John. The old cars used to have the heater control valve in the hose before the firewall. I didn't think the difference would be that big, but it seems to work! But then again, its been hi 70's to lo 80's all this summer here! HaHa Mildest summer in years and the corn is already 7 ft high. I dont use the a/c much, my dog prefers the windows down!