heater blowing barely warm air out of the vents?

Hi,

The cooling fans are tied into the HVAC system as well as the engine temperature. For example, if you place the system in recirculate or defrost, the compressor is engaged to help dehumidify the air in the vehicle. When the compressor engages, the fan turns on if the ambient temperature is above 39F.

Also, certain diagnostic trouble codes that are stored can cause it to turn on as well. By chance, does the check engine light stay on while the engine? If it does and you have a scan tool, first check what codes are stored then delete them. If the light stays out and a code was causing the issue, this should resolve it until the light returns.

Let me know if any of this is making sense. Also, take a look below. You may find it helpful.

Take care,

Joe

See pic below.

Thank you, Joe, that is helpful information.
First, I think I should rule out codes as a problem. No service light is indicating a problem, and this vehicle has been unused (occasionally cranked and moved but untagged partly because of the no heat situation) and at most times with battery unhooked so I believe that resets codes were there to have been any.
Your other line of reasoning seems right on. I also stand corrected on something; the radiator fans do not always come on when I hit the climate control "auto" button. This morning, I rechecked again, and the fans do not act as they had previously. My controls were indicating ambient outside temperature of 35 degrees. Voila! This would have driven me nuts but in your fine explanation you mention the 39-degree point below which they are not initiated. Seems to be confirming your explanation.
I will add some information in that the A/C on this car does not work. Two years ago, I had a shop add refrigerant to the A/C system, learned that the AC compressor leaks refrigerant and that there was some other unknown problem as it would not work. I didn't feel like opening the shop to go on a fishing expedition, so it was never fixed, too expensive. I think the freon is low now and I do not see that the compressor engages if I ask for A/C. I suppose that whatever tells the fans to come on for de-humidification doesn't take into account a non-functioning A/C unit. But I would like a way to interrupt that particular instruction to those fans. I am considering putting the car back on the road but at present the only way I will have heat this winter is pull the fuse or unplug the fan connectors, then pay attention to the coolant temperature. Or keep that ambient temperature sensor in an ice bucket! Thank you, Joe. Have a good day.

Hi,

If the compressor is engaging when you select AC, there must be enough freon in it to allow it to actuate. That will turn the fan on.

Regardless, let me know if there is anything I can do to help.

Take care and keep warm.

Joe