08 Ranger blows hot air, except at max AC

[KD2AQY]

This morning, I had the coolant system on my 2008 ranger flushed. The truck was also in the shop for a bad EGR valve hose. Anyhow, once I got the truck back, I turned the A/C on (it was only 80 out, but the truck had been in the sun for a while). The A/C would only blow hot air. I turned the system to vent, defrost, etc., and while the air was redirected, no matter where I had it set, it was hot. However, when I set the truck to max A/C, then it blows cold air.

I took the truck back to she shop, and they insisted that it was working properly, since the A/C worked at Max. They also said that the only problem that would cause my truck to only blow hot air would be the blend door, which would require them to pull the entire dashboard, which would run up a labor bill of at least three hours. Obviously, I don't want to give those clowns any more of my business.

On one of the heater hoses, there is what looks to be a vacuum actuated valve. There is evidence of coolant leakage beneath it. I do have the Haynes manual, but it is far too general to even mention the purpose of that vacuum valve. So, my first question is what does that vacuum valve do?

I dropped the glove box down, so I can see the blend door actuator (a flat white box on top of an air plenum) as well as the wiring harness for it. Does anybody have a wiring diagram or plug pinout that can tell me what leads to check to see if the actuator is getting a signal?

I've seen youtube videos explaining that in order to get at the actual door, I would have to cut a hole in the plenum with a Dremel. Is that procedure recommended, or would I be better off having a pro take care of this? The truck is only 6 years old, and I still owe over 11K on it, so I don't want to butcher it.

Finally, it there anything that the my ex-mechanic could have done during the coolant flush that would damage my truck's ventilation system?

 

[adsm08]

From the work you said you had done I can't see any way that they caused the problem, short of going out of their way to intentionally break something. Not likely for a business that wants to retain customers.

The valve you are describing is a heater core bypass. It is supposed to shut off coolant flow to the heater core while the AC is on to squeeze a few more degrees out of it, but if it isn't working it will not cause your issue.

If it is blowing hot hot air, like it's being heated, and you have confirmed the compressor is coming on in the AC position, then I would suspect the blend door actuator may be at fault.

If the compressor is is not coming on then the head unit is at fault.


It's not really possible to test the signals for the blend door actuator directly, but if you get cold air when in MAX, then the door is not likely to be stuck. So don't go cutting up your air box.

FWIW I don't ever run my AC on anything but max because you get the most efficient operation from that setting. It takes the already cold air in the cab and recirculates it through the system, instead of bringing in new hot air from outside and having to cool it down from scratch.

 

[cvar]

I cut into the plenum with a utility knife, to fix my B4000's broken blend door. A brand new blend door is $15. To replace it, I basically followed this: http://www.ford-trucks.com/user_gallery/displayalbum.php?userid=131456&albumid=12494

Fwiw, our Linc Conti has a weird blend-door problem too. Anytime the battery is disconnected for 5+ minutes, the blend door sticks at the HOT AIR position, no matter what the temp setting is actually dialed to. The solution is to crank up the heat to the max (90F), then back down to normal (70F), and that corrects it every time. Perhaps it unsticks the blend door? I wrongly blamed the Ford dealership service techies the 1st time it happened (years ago), but now I know it's not their fault.