2001 Silvarado 2500 Hd the temperature control switch does not control temp; it just blows very hot. The A/C does not seem to kick in with the switch tuned on to make the temperature even a little cooler. ^The fan switch works fine. The truck always had a tendancy to freeze the evaporator in the desert and I would just turn off the A/C and let it thaw; could it be that the system has a leak and the freon is low? The why does the temoperature only blow HOT HOT not the ambient temp outside? Thanks for your help Ken

Even though you have a manual HVAC system it still has the capability to set an store DTC'S - diagnostic trouble code's .
DTC B0413 02: Temperature Control 1 Feedback Circuit Short to Ground (CJ3)
DTC B0413 05: Temperature Control 1 Feedback Circuit Short to Battery or Open (CJ3)
DTC B0413 61: Temperature Control 1 Feedback Circuit Actuator Stuck Open (CJ3)
DTC B0423 02: Temperature Control 2 Feedback Circuit Short to Ground (CJ3+C67)
DTC B0423 05: Temperature Control 2 Feedback Circuit Short to Battery or Open (CJ3+C67)
DTC B0423 61: Temperature Control 2 Circuit Actuator Stuck (CJ3+C67)

Did you have Actuator Recalibration done after replacing the actuator or control module ?
Your best bet ,take your vehicle to a qualified repair shop .
Preferred Method (w/ Scan Tool)
Clear all DTCs.
Place the ignition switch in the OFF position.
Install the HVAC actuator.
Connect all previously disconnected components.
Start the vehicle.
With the scan tool, initiate the Motor Re-calibration feature of the Heating and Air Conditioning Special Functions menu.
Verify that no DTCs have set as current DTCs.

This can be a faulty temperature control unit in the panel as it fails to keep control of the settings . If so please try and reset the control from HOT to COLD many times and see if there is any change.
If there is a electronic temperature control- auto climatic control - then this can be a suspect.
Also you must check if the AC cuts off in this condition, check the gas pressure in the display or if the cooling pipes are getting hot. If so the AC must be checked, check the gas , check the presssure switch , the compressor pumping pressure, block in the evaporator.
Thank you for using fixya

No that temperature is not too hot for your engine. The system is apperntly kicking in at 240 from what your saying and then it starts to cool itself down. One of your fans may be going bad if you keep blowing fuses.

Probably the left side air temperature actuator is bad . electric motor that controls opening an closing of temp door in the HVAC case . No the computer doesn't need to be reset .
Temperature Valve Actuator Replacement - Left Side
Removal Procedure
Remove the left instrument panel insulator. Refer to Instrument Panel Insulator Panel Replacement - Left Side in Instrument Panel, Gauges and Console.
Remove the knee bolster. Refer to Knee Bolster Replacement in Instrument Panel, Gauges and Console.

Disconnect the electrical connector from the left air temperature actuator.
Remove the mounting screws from the left air temperature actuator.

Remove the left air temperature actuator.

that is entirely possible yes, could also be a broken cable to change the temp from hot to cold, could be a problem with certain ac components under the dash

There is a door that opens to the heater core.When the vacum control in the dash gets old the diaphram gets to flimsy to close one port so it puts vacum to all ports.Therefore there is not enough pull to engage the vacum motor to move the trap door.Change the switch in the dash. Check to make sure that there isn't an obstructing object in front of the door before you buy a new switch

Everything that is heat and cooling in a vehicle is controlled by vacuum from the engine. It appears to me that your blend door vacuum line to the temp control switch is either off or cracked/broken and not making things work the way you want/expect. It's the vacuum friend.

No ductwork [to the lower vents] under the dash. They are part of the heater core / blower housing is integrated (all one piece).

After reviewing shop manual, we suspect that one of the three damper flaps is not positioning correctly; or debris has blocked one side (which makes more sense given the symptoms).

We're waiting for the temperatures to get back in the plus numbers to check out the physical arrangement.

Notorious for plugged heater cores. Also updated plastic restriction couplers mounted at heater core available from dealer. Try back flushing heater core. Run engine till its at operating temperature then carefully hold the inlet and outlet hose breifly with heater fan on high if hoses are nearly the same temp then flow is good , if not then core is plugged.

does the heater core get hot, check the coolant hoses going to the core to see if both are hot, if they are U have a air temperature control blend door problem, most likely the actuator for the door has failed.