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There several possable causes for this problem here is a list,
Air Bag Control Module (ABCM)Automatic Zone Control (AZC)Body Control Module (BCM)Driver's Door ModuleInstrument Panel Cluster (IPC)Passenger Door ModulePowertrain Control Module (PCM
The following diagnostics would need to be preformed to isolate the problem,
Check the Programmable Communications Interface (PCI) bus signals at the Diagnostic Junction Port (DJP) when the gauges are not working. 2. Disconnect the cap from the DJP and scope check each of the lines. They should all have a 7-8 volt uneven square wave. 3. Pin #1 goes to the Powertrain Control Module (PCM) and the Passenger Door Module (PDM). 4. Pin #2 goes to the Driver Door Module (DDM). 5. Pin #3 goes to the Automatic Zone Control (AZC). 6. Pin #6 goes to the Instrument Cluster (IC). 7. Pin #8 goes to the Body Control Module (BCM). 8. Pin #9 goes to the DLC. 9. Pin #5 goes to the Air Bag Control Module (ABCM). 10. If there is no activity on one of the bus lines, check the wire to the module and that module would be bad.
You would need a trace scope to check the square wave patterns.
Hope this is helpful.
Here is a picture location of the diagnostic junction port where these test are done from.
no cold air blowing out when ac is on but low pressure