heater and a/cgoing crazy

[kebyous]

had battery changed at our local save you money walmart. car was running perfectly fine. now the air conditioner and heater rotate coming on only on drivers side. Passanger side runs hot and not only that the fan is going from high to low constantly. every thing else is working fine. walmart sent me to the chevy house to get dianostic done, that guy said he believes the heater and a/c control head is going out. how could this happen all of the sudden at walmart. could it be the battery,maybe low voltage or something. the battery is running from 12.7 to 13.6 no higher than that.does anyone have a clue. parts store says part is $1200.00 plus programmimg and instalation. walmart denigns it being there fault of course. thank for any help

[HotZ28]

This particular problem was a design flaw in the system and not anyone’s fault, other than the design engineers. When you disconnect the battery with the system ON, you will loose memory settings and the system will generate faults when power is restored, similar to your home computer when you abruptly disconnect the power plug without powering down the system. There is nothing wrong with the controller; this was simply the way it was designed! You can have the system recalibrated @ the dealer, or most high-end AC shops that have the right scanner. If you are patient, it may reset on it’s own after 50 or more ignition cycles, if no further faults are found. The only way to prevent this from happening, is to turn the system OFF before disconnecting the battery! Click Here for some more info.

[Scrapper]

yes mod is right my 87 did the same thing after changing battery and i let it go for awile and it straitened out on it's own.

[ZiggyPA]

Maybe a stupid question, but how do you turn the system off as I presume one changes the battery with the ignition off?

[HotZ28]

Originally Posted by ZiggyPA

Maybe a stupid question, but how do you turn the system off as I presume one changes the battery with the ignition off?

No question is stupid, turn the AC system off before turning the ignition switch off.

[Blue Bowtie]

In addition to disconnection without preparation, as the Hot-Z professes, charging the battery can have consequences.

It is better to charge a battery either out of the vehicle or while disconnected from the vehicle wiring. Many battery chargers impart an AC voltage onto the system as well as DC voltage. The battery itself is presumed to act as a capacitor in that case, but it seldom takes care of all the AC ripple. The positive going pulses on the negative side of the circuits can have an effect on both the CMOS logic and effectively "reprogram" the NVRAM of the controller. This is a rare occurrence, but it CAN occur. Similar problems can occur when a diode in the alternator rectifier bridge shorts instead of failing in an open circuit mode, causing all manner of problems. GM had a TSB regarding the allowable AC voltage on a system, and as I recall, it was something on the order of 0.2VAC. Any more than that can create trouble.