97 C280 HVAC noise, air flaps cycling noise ?

[97 SL320]

I've been driving the 97 C280 lately. The HVAC under dash / passenger side area has an air flap cycling noise when in ECON mode / 65* requested temp / 70* + outside temp. This noise is on a 3 to 5 second cycle like it is trying to regulate something but decides not to.

Would a leaking vac actuator pod do this? As in moves , leaks, moves back, controller responds to correct movement, cycle continues.

I have not yet looked at live data and there are no other odd behaviors.

Thanks

[tinypanzer]

Originally Posted by 97 SL320

I've been driving the 97 C280 lately. The HVAC under dash / passenger side area has an air flap cycling noise when in ECON mode / 65* requested temp / 70* + outside temp. This noise is on a 3 to 5 second cycle like it is trying to regulate something but decides not to.

Would a leaking vac actuator pod do this? As in moves , leaks, moves back, controller responds to correct movement, cycle continues.

I have not yet looked at live data and there are no other odd behaviors.

Thanks

If you can get to the pod, you can test it with a mityvac. In certain situations you can test with a mityvac on the main vacuum line feeding the HVAC solenoids. That will tell you if you're losing air.

But really I wonder if its just a function of the fact that you have set the interior temperature to a lower setting than the outside air is capable of providing. In ECON mode, you're not getting any AC compressor so the only way it can cool the car is by pumping in outside air. There's all sorts of weird climate control logic in that box that tries to regulate not just the temperature, but it also redirects air to the defroster depending on current conditions and whatever it decides is necessary to prevent fogging in most situations.

Do you know which flap is actuating? If it's the defrost/vent flap, you can rule out a vacuum leak on that pod if you can get it to stay in vent mode, say by turning off ECON mode possibly. The vent/defrost flap is designed to fail into the defrost mode when the vacuum pod fails. If you can get it to stay in vent mode for any length of time, I think that proves the pod is good. In that case, there's either something else wrong, or there's nothing wrong and it's the combination of the ECON setting combined with the interior and exterior temps you're experiencing right now.

[97 SL320]

Thanks, I don't know what is moving but I'm guessing it is the temperature regulation flap since the air does not seem to change where it comes out when making noise and I don't hear it in the first few min of driving.

I was thinking that if the temp flap has a position sensor, perhaps it is failing and the controller is cycling thinking it is where it but really isn't. As a side note, the HVAC control panel is the same as a similar year SL, just the version coding is different.

I don't drive this car much as it is Moms summer car and lives at my house during the winter. Will try to see if moving requested temp makes a difference.