89 Climate Fan - Medium Setting mod?

Not sure if this is even possible. To quote someone else from a recent post, "it gets hot around here:mad:" Is it possible to increase the fan speed on the low climate fan setting on an 88 / 89 to more of a medium speed? It seems like often low is too low and high is too high. A medium would be nice. Or I could just by a 90 or 91:) or get a littlle battery operated fan - but that is not preferable. I couldn't find this issue addressed with search..thanks for any ideas.

Cody

Could be done but not easy if you want to keep any of the normal functionality of switching to other speeds and keeping auto mode.

Best way would be to reprogram the BCM to adjust the low speed output voltage over the nominal 4 volt low speed output, but that BCM code hasn't been documented yet publicly.

If you really wanted to do it, I would suggest hijacking the input wire from the HVAC controller to the blower module and replacing with a 12v wire with a switch and rheostat installed that will allow you to control its voltage from 0 to 12 v. That should allow you to dial in the fan speed to anything you want.

Low is around 4 volts and high is battery voltage (12+ volts) So medium would be around 8 volts.

There is a feedback line from the fan motor to the HVAC controller, but while this will upset that controller, (as it's not being in control any longer) I don't see where that will create any issues outside of the controller. No warning bells should sound etc.

I have the opposite problem. My fan stays on either a low or medium speed on my 89 (can't judge the speed because it only has one). How can I correct this problem,

MC_Reatta, thank you for the thoughtful reply. Not sure if I will try this, but it sounds like it would work. I think you would lose the low / high setting and just get one customized speed with either low or high selected if I am thinking about this right.

Correct, you would lose the auto function and the ability to select fan speed via the CRT. You would have only manual control, but you could select any setting from low-low to full speed at your whim by turning a dial.

So Cal, Assuming you have the correct (4pin + 2pin) blower control module installed, I would suspect the HVAC controller is not decoding the signal from the BCM correctly, or its feedback circuit isn't working properly.

Best way to troubleshoot would be to measure the signal from the HVAC controller to the blower module and the from that to the blower motor. Low speed should be ~ 4 volts and high should be 12+. Auto would be somewhere in between. You should be able to hear the difference in the sound of the blower motor even if the airways are clogged with debris and you can't feel a difference in the airflow.

If one were to do this, what would be the best route to get the rheostat wire from the engine compartment to the interior cabin?

No need to bother with getting into engine compartment as wire to blower module originates at the HVAC controller under dash behind glovebox.

You can grab a switched 12 volt source in the fuse box, run it thru a radio switch / volume level control and on to the gray wire coming off pin R of the HVAC controller. That goes thru a grommet in the firewall and out to the blower control module input.

Rethinking, if you used a switched source, having a switch along with the rheostat would be redundant. Turning the level all the way down would stop the fan once the voltage dropped well under 4 volts and since there would be no voltage when ignition is off, you wouldn't have to worry about fan running on draining the battery.

I'd just use a spdt switch - right is auto, left is whatever speed you determine with a voltage divider. Do not have off since the evaporator needs some air flow to keep head pressure from skyrocketing.

Would this type of rheostat work?

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No, that one creates a pulsed DC, it doesn't reduce the voltage.

You need a variable resistor that can act as a voltage divider to reduce the voltage to the blower module by about half.

I'd add that it would have to be a pretty substantial rheostat. I've never measured the current draw of the blower motor, but could be a coupe of amps or so peak. This would require a control with a high wattage rating to prevent the burning it up. Might be better (and a lot cheaper) to get an assortment of large wattage fixed value sand block resistors (at least 20 watt, if not 50) to go in line with the motor voltage lead and then make sure the one chosen is installed such that it is thermally shielded from any surrounding area as it will get hot.

KDirk

I may be willing to try this - but I would need help finding the right rheostat device. I would think once the device was identified the wiring part would be fairly straightforward - I have already spliced my gas / trunk buttons under the dash (as well as keeping the glove box buttons operational) and will post pictures of that soon. I would probably mount the dial right under the dash snug up next to the cassette / crt console in that corner drivers side. It is a fun project to think about.

Cody