heater, low to no heat

Hi, took cap off of flushing tee on heater core return hose, put funnel in radiator and poured in antifreeze until liquid came out of tee, replaced tee cap and radiator cap took truck to steep hill parked and ran for five min at 2,000 RPMs then backed truck up steep hill ran again at 2,000 RPMs for five minutes, took truck for a drive temperature gauge stayed even and heater worked fine! found that the selector switch has two positions that the A/C compressor cycle on and off one is floor and defrost, the other is upper ducts only in recycle mode, but in fresh air heat mode only heat no A/C compressor cycling takes place. hope this helps other people.

That is great info. Thanks for not only coming to 2CarPros but sticking with your issue and fixing it then updating us with what you found. It is people like you that make this site better. Not to mention it appears you figured this out in under 3 hours. Very impressive.

I suspect you had an air pocket that you worked out and that AC compressor cycles in those settings to try and control moisture, so the windshield does not fog. So even when it is in heat the AC will still cycle to remove any moisture. Modern vehicles use a sensor to determine if it needs to cycle the compressor, but you clearly nailed this one.

Great job.