I'm looking at my buddy's '99 convertible. When he turned the key on he got service abs, service traction control, low fuel, I cleaned all the grounds, connections, plugs to rule them out. Then he tells me he had changed the HVAC control unit, pulled it out and turned key on and no messages. Plugged it back up and got them. We ordered another, plugged it in and no warnings. When I hooked up scanner it could communicate with all modules except HVAC. I cleaned the star connectors, no good, still no warnings when key turned on but I still can't connect to hvac unit, every module except HVAC. Is there something I need to do to the new HVAC controller after installing? After sitting a few days the battery was dead, did a amp draw with key off and had half an amp, 500 mills. Checked the glove box light switch, it went bad in my '98, unplugged it and draw went down to 250 mills. Started pulling fuses and I believe it was fuse 25, checked print and all that is on that circuit was a feed to body control module and instrument control panel. Pulled that wire from c1 on body control module (orange wire) can't remember plug position number, cleaned it, reinserted wire and draw dropped to 90 mills. When I leave that wire out of plug draw falls to 20 mills. What am I missing here? Can't find anything else. I would like to get it down to 20-30 mills
Thanks in advance for any help.

 

Why did he change the control panel?

You have not mentioned 12v and ground checks at HVAC panel connector, nor have you mention if it turns on....digital display, etc. Have you confirmed the class 2 wire between the control panel and the star connector is good?

Not sure I follow the logic in depinning the connectors on the BCM....Connect all the wires back up, and start from square one. Pulling fuses on a car that has a BCM that enters a sleep mode is not effective, and can have you chasing your tail..because every time you pull a fuse, you can wake up the BCM again. Voltage measurements across the fuse of concern is the way to go. You also cannot leave the doors open when you are doing this troubleshooting, unless you fake out the lock switch. I would start in the at the battery measuring current draw to the whole car, and see how far it drops when the BCM goes to sleep. A quick isolation method is disconnecting the IP fuse box from the terminal at the underhood fuse box. If you do interior fuses, you have to pull the fuse, close the door, and wait for sleep mode again to see the impact. You are shooting for 20 milliamps (mA).

Pull and post your codes.

 

The first thing to check for any module "no comm" is that modules powers and grounds and looking at the powers and grounds is not the correct way...where did you purchase the HVAC module ??...if EBay that's probably your issue.

 

The lights went out and screen was blank, he sent it out to have new led's put in, got it back and the lights worked but thats when he started getting the warnings, abs, traction cntl and low fuel. Thats when o pulled it out and the warnings stopped, he ordered this one and it works, you can read screen, manipulate doors and go from heat to cool but I cant connect to hvac module.
It has hot and ground to hvac connector, the com wire is good from connector to star connector
I pulled that pin from connector to verify that it was in fact the draw, when i connected c1 to bcm and checked draw and it was 20mills.
I have negative battery cable unhooked just putting my meter in series with battery and cable, when i pull a fuse the negative cable is unhooked, I pull fuse, close door then hook up meter.
With the wire out of c1, doors closed, hook up meter it settles on 1500 mills, after several seconds draw drops to 750 mills, after a few seconds it drops to 500, a few more seconds it drops to .02. with the wire in c1 it does same except it stops dropping at 90 mills not sure which modules going to sleep at each drop. Is there a way to tell which module is going to sleep? Im taking all readings with meter at battery.

 

It has power and ground a hvac connector. I dont understand, you say first thing to check powers and grounds, then say looking at powers and grounds is not the correct way. What is the correct way? Im not sure where he got it, he just dropped it off.

 

Many I see on this Forum "look"...not test !!...so how EXACTLY would check a ground ??

 

Just went out and can connect to hvac module if car is running but not with ignition on and engine off

 

All modules have a battery feed (keep alive) and an ignition feed (wake up)...have you checked Fuse 27 for power at the fusebox AND at the module ??

 

Yes, I have constant hot, switched hot and ground at HVAC control module connector. Maybe a quarter ohm resistance on communication wire between HVAC connector and star connector

 

With key ON you should see a 0-7 volt square wave on the communication wire when using a labscope...with a DMM you should see a fluctuating voltage of maybe 0.2 to 0.8 volts...you will not see 7 volts because a DMM's refresh rate is too slow...don't know how you checked your powers and grounds but if you say they are good they are good...where did you get this HVAC module ??

 

Im not sure where he got it, he said he had ordered one and brought it over when it arrived. l'll have to ask. Not going to be able to get to garage until friday. Thanks for the help.

 

The video has some good information in it. Thanks