You should probably also check your heater core valve. Mine would not close properly and continued to allow hot coolant through the core resulting in the same problem you described.
There are two ways to check this. An easy check is to adjust the heat to maximum, feel the heat coming in by the floor, then reduce the temperature lever to minimum and see if the temperature of the air coming in is reduced. Another way is to block the input (I inserted a steel ball bearing in the inlet hose) or bypass the heat exchanger by connecting a section of hose from the input hose to the output hose in front of the firewall and then see if the heat entering the cabin stops.
If the heater core valve is the problem there is info in the Technical manual to check if it is installed correctly and / or replace it. Replacement valves with the appropriate washers are readily available through several 113 part suppliers.
Good luck.
Norm