dual climate controls

[BigJake37]

Hey guys

My name is jake, I drive a new body style 07 Z71 1500. Ok need some help, my heater only works when its on 90 it blows hot but when I put it to 89 it blows cold air, it also does the same when I start it automatically it blows cold air full blast. Any one got any ideas???

[efritz]

Does it do it on both sides? You may have a cabin temp sensor that failed resulting in it getting a faulty reading and thinking the cabin is already hot when you start so it blows cold to cool it down. 90 degrees just commands full heat.

[oldscsc]

Does it do it on both sides? You may have a cabin temp sensor that failed resulting in it getting a faulty reading and thinking the cabin is already hot when you start so it blows cold to cool it down. 90 degrees just commands full heat.

Bingo! Your heater works on full hot because the HVAC module ignores the in car temp sensor's reading and commands the blend door actuator to the full hot position.

 

You can check the in cabin temp sensor in two fashions. The first (and easiest) would be to get a hold of a Tech II and read the data the HVAC module is receiving. Check the in car temp sensor and its value is likely to be way out of whack.

 

The second way would be to ohm the sensor out. This sensor is actually a thermistor...meaning its resistance changes based on temperature. Temperature goes up, resistance goes down. There are specs in the service manual to compare your readings to. Breathing on it or putting it over a heater vent will decrease its resistance..put it outside or over an A/C vent will increase its resistance.

[BigJake37]

Next question, where is the cab temp sensor located in the truck?!?!

[gmtech4]

try a battery disconnect ,reconnect ,turn key on ,let HVAC cycle thru its relearn bs ,and recheck function ,,if the the same ,,,have a shop scan HVAC module for DTCS ,diagnose and fix it

[TooTall1]

Cab temp sensor is right by the drivers head in the headliner.