It’s worth mentioning that many vehicles have what is called a heater control valve, which is used to regulate the flow of coolant through the heater core. This shuts off the flow of hot coolant to the heater core during the summer when you're trying to run your AC. You wouldn't want your cold AC air to pass through a hot
heater core before it enters the passenger compartment, so this heater control valve regulates coolant flow into the heater core. If this valve has an issue, it can cause no heat or AC that doesn't cool enough.
The AC not cooling enough is very rare. In fact, there is a blend door inside the HVAC system that regulates air flow past the heater core and AC evaporator. I’d look at the blend door before I looked at the heater control valve for a problem like that. It's more likely you’d have a problem with no heat if the heater control valve failed. I've seen these valves controlled by cables, vacuum, and sometimes electronics. Consult your service manual on how to inspect and service them. A quick test to see if it's working is to feel the hose before and after the valve. If it's the same temperature after the valve, it's open and working fine. You must have the heat on when doing this test. If the outlet is cool or cold and the inlet is hot, look to the valve for the issue. It might not be the valve’s fault though. Be sure to check what controls the valve to be sure it's working properly. If the valve doesn't get a signal to open, it won't open.