AC and temperature gauge do not work and drivers side vent blows hot air. If you disconnect battery and reconnect AC is fine except for drivers side vent. The AC then works for several trips and then suddenly temperatures gauge goes to 0 and AC shuts off. Interestingly pulling all of AC fuses will not rest AC , only disconnecting the battery

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#12831 Closed 2008 Chevrolet Trailblazer public

6 cylinder engine


More than likely the service engine soon light is also turning on and there will be a code P0125 or P0128 stored for a faulty engine thermostat. If either of those codes set GM’s strategy is to turn the compressor off to reduce the chance of overheating the engine and to drop the temperature gauge to full cold to get the driver’s attention that something is wrong. The drivers’ side vent temperature staying on heat could be cause the recalibration procedure has been interrupted or the actuator is faulty. Disconnecting and reconnecting the battery begins the recalibration procedure. You can follow the general outline for recalibration in this article. You can continue to disconnect the battery rather than removing the fuse  to begin the recalibration. Trailblazers and Envoys need to have the HVAC B fuse in the rear fuse box removed to start the recalibration process using the fuse removal procedure.

HVAC Actuator Recalibration Procedure For GM Trucks and SUVs

My OBD reads code of ISO9141 and Kwp 2000
I switched relay for AC and disconnected and reconnected battery and AC worked for 1 hour and then temperature went to 0 and AC stopped. No engine light on dashboard.
I have no idea what to do


ISO 9141 and Kwp 2000 are not codes. They are describing the protocols the tool and vehicle system use.

I have mentioned several times that you probably have a faulty thermostat in your engine that would be confirmed by having the codes checked.  It seems your code reader is not up to the task. Most big box parts stores will check the engine codes for you.

The fix is to confirm one or both of the codes are present and then install a new thermostat in your engine.  This is a very common symptom in GM vehicles after about year model 2003. If for some reason one of those two codes are not setting someone will need to look at cooling system data with a scan tool to see what temperature issue is causing the PCM to turn off the compressor and temperature gauge.

I will take to Autozone when check engine light comes on again. For the sake of clarity I think you mean temperature sensor not thermostat the latter being a mechanical part and therefore not effected by disconnecting battery. Please confirm.
Thanks again for your help

I now have code P0128. Does this mean thermostat or ECT?


Your Vehicle is intelligent enough to know that the engine is not heating up properly. 99% of the time it is caused by a thermostat leaking coolant when it is supposed to be closed or simply opening too soon. Check your coolant level and if okay replace the thermostat.

My coolant level is perfect. Talked to Auto repair shop andthe 40 year expert said he was 96% certain it had to be ECT not thermostat.He also said that P0128 code should not be reset when I disconnect battery and it is permanently stored until erased and disconnecting battery will not erase.

So I know have two experts suggesting two different solutions
The other expert said Thermostat would never turn off AC and only bad ECT would do that.

May I have your rebuttal.

More info
The guy at shop I was going to take it to said it would shut AC off only if it runs hot


Not going to get into a pissing contest with you or your expert but I strongly suggest that both of you read the enabling criteria for setting a P0128 code in a GM vehicle and what actions the PCM takes when it sets the code. For that matter just do a Google search then change the thermostat and be done with this problem.

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