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My wife has a 1999 Honda Accord. The buttons that let you switch the ventilation between face/feet/defrost don't work. It is stuck on face so you can't defrost in the morning. The buttons for face, face/feet, and feet don't seem to do anything. The lights for feet/defrost and defrost buttons will light up when you push them, but nothing changes. Is the whole control unit bad? Or is it possibly just a fuse or something else?

Interior of car with buttons highlighted

  • Usually A/C refers to air conditioning compressor, which cools (and dehumidies) the air. What you're referring to can be beter described using the term "ventilation". Just by reading the title I thought you couldn't switch the A/C compressor on/off. – juhist Feb 3 '17 at 15:35
  • @juhist I edited the title and question and replaced A/C with ventilation – Kevin Feb 3 '17 at 15:42
  • Do the heating and cooling both work? i.e. it will blow cold air on cold and warm air on warm (just not where you want it too)? – Zshoulders Feb 3 '17 at 17:11
  • Yes, I believe they both work. Obviously haven't used A/C much recently. – Kevin Feb 3 '17 at 17:12
  • @Kevin wish I could say the same here in California! – Prodnegel Feb 3 '17 at 23:10
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Put the HVAC unit into diagnostic mode and it'll tell you what you should be looking for.

Key On Engine Off, turn off the blower motor, place the temp control knob all the way to full A/C the recirc light will come on. Press and hold the recirc button and the light will turn off. Keep holding the recirc button until it starts flashing.

1 blink is for the air mix motor.
2 blinks are for the mode control motor.
3 blinks for the evap temp sensor.

On this year Accord the mode door is cable controlled by an electric motor. Take a look under the left side of the dash and you should see a 7 pin connector for the mode control motor.

Hit a button, does the motor move? if it doesn't disconnect the motor and apply power and ground to pins 1 and 7 this should place the motor into the defrost position. If it still doesn't move replace the motor. If the motor does move you'll need to remove the control panel and check for continuity between the panel and mode motor. if the wiring and motor check out replace the control panel.

  • Finally got around to taking a look at this, but now none of the lights are coming on on the control panel. Checked the fuse and it is fine. – Kevin Feb 19 '17 at 14:59
  • " apply power and ground to pins 1 and 7" Would I do this with a volt meter – Kevin Feb 19 '17 at 15:07
  • @Kevin You need to jump power and ground with some wires and pins. If the hvac controls aren't lighting up or working there may be another fuse for the unit. – Ben Feb 19 '17 at 15:12
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It's a vacuum line. Rubber tubes run behind the firewall to control the vents. A rubber tube has likely deteriorated over the years.

You can look for the tubing under the hood, coming out of the firewall. Oftentimes, a tube will disintegrate near the hot parts of the engine where it obtains its vacuum source. If not, you will have to remove plastic cowling over the firewall and trace the tubing deeper into the dashboard.

  • Can this mean that in the worst case you will have to disassemble the dashboard? – juhist Feb 3 '17 at 17:46
  • I'm pretty sure manual hvac on this year accord is cable operated and not vacuum operated. you may want to double check your service info. – Ben Feb 3 '17 at 21:18
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I'm not 100% positive on this, but I think the blower door actuators are electric on the accord, not vacuum. To test this, I sat in my 01 Accord (same car different year). With the key in the accesory position (no vacuum), I can switch between all of the different blower configurations with no problems. You can even hear the little doors moving around in there.

So get in it, put the car in accesory mode, and try to switch between the various buttons. If you don't hear anything, my guess would be the vent door actuator motor is toast, or whatever fuse it is on is toast. Not sure what fuse that is exactly, but you can look at the fuse diagram in the owners manual.

From what I've found online, it doesn't look like you need to pull the whole dash apart. The part under the center control console has a few screws holding in the trim that allow you to get at these elements. Hopefully.

  • I'm pretty sure that's the heater core flow valve and cable. – Ben Feb 4 '17 at 0:24
  • @Ben You're absolutely right, I've edited that part out so nobody gets confused. – Zshoulders Feb 13 '17 at 16:27
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I had this happen to me right after I replaced some engine mounts. The power to the HVAC control panel would be intermittent.

I tried changing the panel but no luck. Still intermittent power.

I traced it to my bonding straps and battery ground cable. I replaced a couple of the engine bonding straps and cleaned all the the connectors on the ground cable and it works fine. Give that a shot. Lights came on right away and was able to switch functions again.

Luke

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The mode control motor is easily visible from the driver's foot area. It's on the side of the center console. Change the setting on the control panel to bi-level (Def/Foot) and wiggle the control rods until they move to the bi-level position. This will hold you until you receive your new MOTOR ASSEMBLY, MODE- 79140-S84-A01 which you can get from any Honda parts source, in person or online.

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