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I have a situation where only the Max AC function doesn't work. It's my understanding that this simply controls where the air intake comes from, but when I move the slider to that position, nothing happens. The blower doesn't turn on at all; it's like it's still in the off position. I can hear a very slight vacuum noise, but nothing else. All of my other HVAC functions work. Regular AC, bi-level, vent, heat, and defrost all seem to work as intended. The blower motor fan speeds appear to be all different - just nothing happens when I try to use max AC. Last year I spent a lot of time (and money) getting the AC to work and at one point max ac did work, but I don't know what has changed. Any ideas?
The relay on the right in this picture. Just had the same thing happen. I had trouble finding the same one with the correct pin layout so I got this one. It was ultima brand from oriellys.
If his fan works in all other modes except Max AC, the relay is functioning fine. The HVAC control uses the same fan relay/speed control in all modes. Sounds to me if nothing happens except the vacuum motor being actuated in Max AC then it is the HVAC control itself having a issue.
All I know is that when I swapped that relay mine started working on max ac when it did not before. Now, if it happens to be a wire jiggle of something in the swap out that actually cause it to work, I don’t know.
The relay shown is the high speed fan relay. It only controls high speed function of the blower motor.
Max AC compared to AC mode recirculates air from cabin. That is the only difference between the two. Which is controlled by the vacuum actuator on the flap door. Electronically it is the same for both modes. Sends 12v on its path through the various AC components to the clutch and then sends 12v through either the orange wire when in high fan setting or the other wires for 1/4 speed, 1/2 speed, 3/4 speed that goes to the fan speed resistors.
That’s fair enough and I’m not arguing with you. All I can say is that I could have fan on high with the selector on norm and it would blow away. If I left fan on high and selected max ac the blowing would cease. Changed out that relay and it started working. Could have 100% been a cawinkidink as I was working right next to the blower resistor. Do you think that is more likely what happened?
One thing I have not tried is different fan speeds for Max AC. Usually, I've just got it on high all the time. I'm curious if having it set at a lower speed would change the results. I suppose it's possible that the "high speed" I'm seeing is not actually high, but I would assume that it wouldn't work in that setting, not just spin at a lower speed.
