Occasionally when I start my car, the heater/AC will not blow. I have tried turning the heater/AC off and back on, changing the fan speed, changing between defrost/floor heat/etc, but none of that makes a difference. The problem only happens about once every week or two. Last time it happened there was frost/fog on the windshield in the morning and my defrost wouldn't blow! But then on the way home from work it was working fine.

I’m posting this in the electrical forum because I think it is a problem with the part of the electrical system that turns on the blower. But I don’t really know what is wrong or how to fix it. Any suggestions?

Car: 2003 Bonneville SE 3.8L V6

you have auto or manual controls? either way there are a few things it could be and until its broke its hard to tell which

Manual climate controls.

What are some things to check the next time this happens? Are there some places I could inspect for frayed wires, etc? Are there likely to be any fault codes reported?

when it fails i would check power at the fan for one, purple to black, if its there your fan is bad. if not have to trace it back;

I am not a bonneville expert however: if you have manual climate control you probaly have a vacuum line running from your intake to a vacuum resevoir on the fire wall. Check this line and make sure it is not cracked, leaking, disconnected or somehow leaking vacuum. Without adequatge vacuum your manual climate control will not work. Just fixed my 94 Lesabre, had a old hose did not fit tight and caused intermittent climate control problems.

I removed the panel covering the blower motor. It turns out that panel is at the feet of the passenger seat. So I started keeping my voltmeter in the car so that when it failed I could measure the voltage across the motor supply voltage input. It has failed only twice since then. I never did get to the point of measuring the voltage because I have found that when I lightly bump the connector, the motor immediately turns on. So I think this means there is a poor electrical connection somewhere at the motor supply voltage input. Does that sound right?

Well I would say, possible; however most likely is that your blower motor is on its last leg. Evey blower motor has a specific life span and that is directly related to how much of the brushes are remaining to contact the armature. When the brushes are almost gone they do not make contact as needed to transfer the appropriate amount of DC current to get the motor turning. Next time the motor stops don't do anything except remove the plug, test it and see if you have power. You got power than you know it is just your blower motor ready for the graveyard. Can not get it changed rite away, keep a stick handy to hit it to get it going and don't shut it off... LOL

You should inspect the contacts in that connector and the plastic around each one. Some poor contact on one carrying heavy current heats it up and melts the plastic around it and also deteriorates the metal contact surface. The melted plastic means the contacts are being held in place like they should be.

Also, try tapping only on the bottom of the motor even fairly gently with the tip of your shoe when the key is ON and the blower won't work. A little vibration there can also vibrate the connector that may be your problem. So some differential diagnosis is needed.

My 03'* blower was easily replaced with 3 screws and a rubber tube for cooling the motor to handle. I used a towel to hold new on up as I tried to get a screw started. Otherwise, just the lying upside down is the only negative.--and $139 for an Autozone replacement.