Chrysler Repair: air bag light and no heat, heater cores, wire harnesses

Question
I have a 1993 Grand Caravan 3.3 and after replacing the alternator the air bag light came on and the heater just blows out cold air now. It has rear heat which was blowing out heat but the front vents were cold. It does have a heat control valve on the firewall which i wired open and then got some heat to the front but now none to the rear heat. It always has had problem blowing out cool air when stopped at stop lights or just idling. There is a small vacuum line to the heat control valve. Is there something i may have done to make the heat not work and the air bag light to come on while replacing the alternator.

Answer
Hi DeWayne,
I don't see a connection between the alternator replacement and the air bag warning light coming on. About the only relationship is that both are electrical circuits, but aren't really logically interconnected except through the overall battery system. There are impact sensors mounted on the left and right sides of the engine compartment just below where you see the hood bumbers sticking up from the radiator crossmember and those have electrical connections; but if you didn't disturb those wire harnesses in the job those shouldn't be the cause. More likely is that by chance the clockspring connection between the steering column and the steering wheel has suffered fatigue such that when the restraint computer module attempts to verify that it can 'see' the airbag it is finding that clockspring circuit to be "open" so that light would be an alert for that reason. The clockspring flexible electrical connector does sometimes wear out.

On the heating, as you know, the vacuum line to that by-pass valve has to be connected or the valve may open and send the heated coolant back to the engine without flowing through the cabin heater cores (front and rear). So you will want to check that you are getting hot coolant going into the cabin and back out by touching the two hoses at the firewall after driving enough to get the temp gauge reading normally in the mid-scale region. Then touch the hoses to feel if they are hot, and about equally hot if you are getting flow into the cabin. If one (or both) is quite cool then you aren't getting flow which could be the valve or crud in the lines. If you suspect the lines you could remove the hoses and back flush the system in the cabin with a garden hose. The temp door control is operated by a mechanical cable so you should move the lever to be sure it is still connecting to the temp door in the underdash box. If it feels detached then you will want to check that out. The manual describes the steps to get to the temp door and cable attachment point on the door lever but it is too detailed for me to type in here. I can xerox copy and postal mail you the pages about that if you will send me a postal mailing address.
It would be good too to check over the vacuum lines that branches off of the power brake canister (one to the valve/one through the firewall to the air box under the dash) to see if you can find a detached hose or a cracked line or fitting somewhere in that vacuum operated system. The vacuum actuators control the air distribution but not the temperature of the air coming out but that could be a factor too in the lack of heat.

I hope this helps you narrow down the problems.
Roland
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