My 88 Fox seems to always provide heat inside the car from the heater core. Some days worse that others. Yes, the user temp selector is in the middle field between blue and red. Yes, I tried it all the way to the left in the blue field as well. This has been going on for many years since I got the car 12 years ago. It has AC. Its been checked for low and high side pressures. Its been evacuated twice. Its been topped off each year. The best cool temp inside the car will match summer shade temps.
Went down to the hardware store and got a male 3/4" to female 1/2" zinc coated pipe adapter, and a 3" long 1/2" threaded zinc coated pipe, connected the 2. Also got 3' of 1" heater hose, and same length in 3/4" heater hose and new hose clamps. Jumpered out the heater core by running the 1" hose from the port off the rear of the head to my pipe adapter, then from that to the 3/4" hose, routed and connected to the pipe at the back of the engine behind the oil filter housing. No apparent leaks or drips.
Now the AC can and does cool the car to a more tolerable temp since its not fighting the engine's coolant heat inside the car.
Unlike the conclusion of the Mythbusters TV program, my car does obviously use more gas while using the AC. Its working alot harder on hilly terrains. Acceleration is more labored, and takes longer.