Replaced Battery - Issues With A/c Now

May 6, 2007

Okay guys, I suspected the battery was going bad since it was starting to crank harder lately. Went to auto parts store and they tested it in the truck and it was indeed bad. Replaced it in the parking lot. Now the A/C is whacked out. When I started out and left the blend door was banging like crazy for about 30-45 seconds. When it stopped I could hear the fans running hard but no air from the vents? Air is flowing from the defroster outlets even though the Climate Control is in auto and defrost is not selected. I shut it off, played around a bit at home and tried it again. Same thing, lots of air from the vents and lots of banging. When the banging stops so does the air from the vents.

Hmmmmm. Any help?

Thanks,

redvett · May 6, 2007

Try rehooking the neg. battery cable and make a postive/steady connection and make sure your cables are clean & greased.

98 Z71 SLT · May 7, 2007

Agree with above reply.

Also, keep the engine running, and you may have to "re-learn" all the HVAC mode positions. Cycle thru all the temps AND all the modes to re-learn the HVAC control module.

J45p3r · May 7, 2007

I've heard about this happening before so I went and did a search for you. This was posted by GM-Tech at the Avalanche Forums http://www.chevyavalanchefanclub.com/cafcn....html#msg825424

There is a better way... selecting "recalibrate HVAC" with a Tech 2. Roll Eyes

This normally doesn't happen at all though. In some cases, door flex and/or compression of the seals causes a door to travel farther than the HVAC controller expects to see. If the door counts are not within a certain range when it goes through a forced recal (like when you disconnect the battery), the control head says, "Whoa, something's wrong" and forces the door to the default position, which happens to be heat for a temp door. Finally, after disconnecting and reconnecting the battery enough times, the door finally stops in a position the control head is okay with and all is well again.

This is not common on our trucks, but a couple car models are famous for this. We live in fear of disconnecting a battery on an Olds Intrigue. These always end up like yours and I've spent an hour or more trying to get it working properly again. Some we have never fixed through the usual "relearn" procedure. There's even a new control head for these that are *supposedly* more lenient in their allowance of doors that might go past the zero mark, but they don't always fix it either.

Note that it's very important not to touch ANY control on the HVAC control head while it is going through it's recal procedure. In other words, after reconnecting the battery and starting the vehicle, give it at least 1 minute before you mess with anything.

May 7, 2007

Hey thanks guys. My search on "blend door" got me nothing. Guess I shuld have been more persistant (and less lazy). I'll give the battery thing another try and then take it to the stealership for a Tech II relearn if necessary.

Thanks,

redvett · May 7, 2007

Agree with above reply.

Also, keep the engine running, and you may have to "re-learn" all the HVAC mode positions. Cycle thru all the temps AND all the modes to re-learn the HVAC control module.

Never ever keep the engine running while unhooking the neg battery cable. For one its hard on the alternator and can cause surges in electrical equiptment. The ides with unhooking the neg. battery cable is to unlearn the memory and let it relearn. If everything else is OK nothing else needs to be done. No relearn with a Tech 2 should be needed.