2001 chevrolet silverado 1500 climate control won't always switch to heat

Dual climate control on these is not a manual valve adjuster. It is done electronicly with a electric motor on a valve instead of ran by a maual cable. Find this and check the plug for a 12 volt signal. If you are getting a signal replace the valve, if not it could be a blown fuse, cut wire, or a bad climate contol switch.

Ignition off, remove the hvac fuse for ten seconds, reinstall, start vehicle.

there is a flapper door that is controled by a little servo motor under the dash that controls the mixture between hot and cold depending on where u have the control set. sometimes when that stuff goes out you may hear a thumping sound under the dash... problem could be in temp control switch, the air mixture control door motor,,, if not......heater core could be stopped up or bypassed underhood

the heater radiator could be blocked or the valve controlling the heater could be faulty ,,,, carefully check the heater hoses ,, they are the small ones running from the engine bay through the bulkhead into the car,,,they both should be hot ,,, if one is cold the water is not circulating either due to a blockage or the heater valve not working ,,, if the car has climate control you need to be sure that it is serviced properly as this system mixes the hot and cold air,, also at 210 you should have some heat , the best way to check if its the thermostat is to run the carstationary until it gets hot even if the thermostat is faulty the system will build up heat due to no cold air passing through the grill and coolng the engine radiator

dont quote me here but i think you may need a new computer for the climate control ? bit hot though isnt it if set to 90?C

If you have duel climate controll and by this side you mean the drivers side then will tell you that I ended up replacing the controll unit and fixed the problem,When mine would go from cold to hot I would turn off the key then it would go back to normal until I hit a bump or adjusted the heat slider. there are two one on each side of the trans hump.I just went to dealer and asked for a printout of the parts break down.It is way up under there from what I can remember.Well hope this helped a little any way.

The fan module just above the heater motor likely needs to be replaced. Sometimes the connector that goes to it melts as well.

check switch and under dash controls for disconnected or damage

check the coolant make sure it's full check to make sure your engine temperature reaches normal operating temperature if not then a new thermostat may fix the issue. if the engine does reach operating temperature the check to make sure the blend door under the dash is working properly

Had the same problem with my Mazda6 awhile back. Took it to the dealer and they found the radiator wasn't holding pressure. They replaced the whole radiator under warranty (WHEW!). Not sure how to check for that kind of thing, but it's a start.