Here's a breakdown of potential causes, ranging from most likely to less likely:
1. Low Refrigerant: This is the most common cause. If the refrigerant level is too low, a pressure switch will prevent the compressor from engaging to protect it from damage. This is the first thing a mechanic will check. A leak somewhere in the system is the likely cause of low refrigerant – it's not simply a matter of adding more.
2. Faulty AC Compressor Clutch: The compressor is driven by a clutch that engages and disengages. This clutch could be failing due to:
* Worn Clutch: The clutch may be worn, preventing it from engaging.
* Bad Clutch Relay: The relay controls power to the clutch. A faulty relay prevents the clutch from receiving power.
* Bad Clutch Cycling Switch: This switch senses the pressure in the system and tells the relay when to engage the clutch.
* Shorted Compressor Wiring: Check the wiring harness going to the compressor for shorts or damage.
3. Problems with the AC System's Electrical Components:
* Blown Fuse: Check the fuse box for a blown fuse related to the AC system.
* Faulty AC Pressure Switch: As mentioned above, this switch prevents the compressor from engaging if the pressure is too low. A faulty switch might not work even with adequate refrigerant.
* Problems with the AC Control Module/ECU: The control module manages the AC system. A malfunctioning module could prevent the compressor from engaging. This is usually a less common issue.
* Faulty Blower Motor Resistor: While this doesn't directly control the compressor, a faulty resistor can sometimes affect the whole AC system.
4. Problems with the AC System's Mechanical Components:
* Seized Compressor: The compressor itself might be seized, preventing it from turning. This is a more serious issue requiring compressor replacement.
* Faulty Expansion Valve or Orifice Tube: Restriction in the flow of refrigerant can cause low pressure and prevent the compressor from turning on.
Troubleshooting Steps:
1. Check the refrigerant level: This requires specialized tools, so take it to a mechanic unless you have experience with AC systems.
2. Check the fuses: Locate the AC system fuse(s) in your fuse box and check for any blown fuses.
3. Check the AC clutch relay: Have someone turn on the AC while you listen for the relay clicking. If it doesn't click, the relay might be faulty.
4. Listen for the compressor clutch: When the AC is on, you should hear a faint clicking sound as the clutch engages. If you don't hear anything, the clutch isn't engaging.
5. Visual Inspection: Visually inspect the compressor and its wiring for any obvious damage.
Important Considerations:
* Safety: Working with refrigerants requires specialized knowledge and equipment. Improper handling can lead to injury or environmental damage. It's best to have a qualified mechanic diagnose and repair your AC system.
* Cost: The cost of repair can vary widely depending on the cause. A simple blown fuse is cheap to fix, while a compressor replacement is significantly more expensive.
If you're not comfortable working with automotive electrical or AC systems, take your Blazer to a qualified mechanic for diagnosis and repair. They have the tools and expertise to safely and efficiently identify the problem.
