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Old 05-29-2020, 11:50 AM   #2
fdryer
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Join Date: Jan 2006
Location: NYC
Posts: 45,303
 

2003 L-Series 3.0L Sedan
Default Re: HVAC not functioning

Some easy things to check before visiting GM or a reputable ac repair shop.

1- check for a blown ac fuse.

2- If the fuse is fine, either have someone turn on ac while you observe the ac compressor engage with a metallic click or listen carefully for it as you turn on ac with the engine idling. All ac compressors use an electric coil for clutch to engage the free spinning pulley. The clutch plate moves a few thousandths of an inch when engaging and usually makes a loud click from metal clutch to metal pulley contact. If you do not see or hear the clutch engage, this may be loss of refrigerant issue - a leak releasing refrigerant, oil and dye.

Normal wear and tear occurs with many ac systems failing from inevitable damage with a leak occurring. When enough refrigerant is lost, a pressure sensor detects the loss and sends a disable signal to the ecm to disable compressor operation. The sensor protects the compressor from self destruction. GM made it easier for mechanics and diyers when dye was installed at the factory. Dye mixed with refrigerant oil circulates throughout a system so any break or weakened seal releases refrigerant, oil and dye with dye marking where damage occurred. An inexpensive uv blacklight will make fluorescent dye glow to show where damage occurred. Removing one or both service valve caps should reveal some refrigerant oil and dye (greenish yellow).
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