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Intermittent Heat. 97 Ford Ranger 2.3l

There used to be a audible pop in my stereo speaker when my heat would kick on. Now there is not. My heat did this last winter around the same time. I checked Fuses. The blower blows, but it just blows cold air. It could be a thermostat, or a clogged heater core.

Any suggestions would be appreciated, especially some troubleshooting steps would be nice.

Thanks in advance.

If you have a temp gauge and it is going up to normal operating temp, it is not the thermostat. Looks like blend door problems are common, http://www.therangerstation.com/Magazine/Summer2009/blend-door.htm There is also a heater control valve you may need to check. http://www.ford-trucks.com/forums/570448-heater-control-valve-location.html An easy way I would check the control valve is to check the temp of the hoses going to the heater core, if one is hot and one is cold, that (or a plugged heater core, less likely) is your problem, if both hot, then I would go after the blend door

To add to the good post above, it’s possible the “pop” you are hearing isn’t coming from the speaker, but a blend door on the fritz. All auto HVAC’s pretty much have doors to direct the airflow, on older models these doors are manually actuated by the driver via a cable. Those rarely fail. But on newer vehicles these doors are often electronically actuated, often w/stepper motors. Those door actuating motors can get weak, or the gears can strip, and the result is a popping noise. Next time you are hearing this, see if the “pop” responds to the volume control on the stereo. If not, the noise is probably the motor attempting to open the blend door and failing.