* Blend Door Actuator: This small motor controls the direction of air (heat, cold, defrost, etc.). A failing actuator can make popping noises as the gears inside strip or the motor itself struggles. When it fails, it can get stuck in a position that only allows cold air.
* Heater Core: This is a radiator-like component that heats the air. If it's leaking coolant, you'll lose heat and might even see a puddle under the vehicle (or low coolant level). The popping sound isn't directly associated with a bad heater core, but if there's a blockage or extreme corrosion it *could* contribute to unusual noises. A leak in the heater core would also explain the lack of heat.
* Vacuum System: The blend doors are often controlled by a vacuum system. A leak in the vacuum lines can prevent proper operation of the blend doors leading to only cold air. This could also cause strange noises if there is air leaking into vacuum lines.
Troubleshooting Steps:
1. Listen Carefully to the Popping: Try to pinpoint the location of the popping sounds. Is it consistently coming from the same spot on the dash? This can help narrow down if it's the actuator or something else.
2. Check Coolant Level: Inspect your coolant reservoir. Low coolant, especially if it's happening consistently, strongly points towards a leak in the heater core.
3. Check for Leaks: Look under the vehicle, particularly on the passenger side of the firewall (where the heater core is usually located). Look for any signs of a coolant leak (wetness, rust, or a puddle).
4. Inspect Vacuum Lines: If you're comfortable doing so, examine the vacuum lines running to the HVAC system. Look for cracks, loose connections, or any signs of damage.
5. Test the Blend Door Actuator (Advanced): This involves accessing the actuator (often requires removing parts of the dash) and manually testing its operation. It's a more involved task and requires some mechanical skill and knowledge. Many online videos detail how to do this for the specific year and model.
Likely Culprit and Next Steps:
Given the popping sounds and loss of heat, the blend door actuator is the most likely culprit. However, a failing heater core cannot be ruled out. Start with the easier steps: Check the coolant level and inspect for leaks. If those checks are negative, you'll likely need to investigate the blend door actuator. This might require some disassembly of the dash, so consider seeking professional help if you're not comfortable with auto repairs.
Important Note: Before attempting any repairs, consult a repair manual specific to your 1995 Chevy Blazer. This will provide diagrams and instructions to help you safely access and repair the system.
