2007 Impala LT climate control panel replacement?

[automan9482]

2007 Impala LT 3.5L Flex Fuel, 119K miles.

Several months ago the A/C on this car suddenly stopped working. Upon starting the car it just failed to come on. The A/C button on the control panel would blink 3 times when pushed, and the blower runs, but the system wouldn't engage; I was thinking maybe an internal problem, or maybe the compressor died.
I relayed the problem to a friend of mine who works on automotive and heavy machinery electrical systems, and he was nice enough to run some diagnostics for me. He comprehensively checked the entire system and determined the interior control panel switch itself was faulty.
So I intended to replace the control panel with a used part and got it removed. But while later browsing thru the Haynes manual I noticed a caveat which gave me pause.
The manual says "If the heater/air conditioner control assembly is replaced, a special scan tool is required to program the replacement unit."

Does anyone know if this is true? If so, is there a trick or some way to "program" the replacement part without the special scan tool that I don't have? Removing the old unit was pretty straightforward, and I assumed the replacement would be plug and play until I saw that.

FWIW I'm including a pic of the original part for clarity...
Many thanks in advance.

[Stealthee]

Knowing GM you probably need a Tech 2 to make it work with the replacement.

[brcidd]

Blinking a/c light usually means a code is set due to low refrigerant in the system--did you ever see how much refrigerant you have in your system?

[automan9482]

Stealthee: Thank you!

brcidd: I did consider that 1st. I had seen the blinking light meant the system was possibly low on R134a. But when I attempted to add refrigerant the gauge supplied with the EZ Chill refrigerant pegged into the Red Zone, indicating (according to the gauge) Possible Mechanical Problems. That is what made me initially think "compressor."
The A/C was blowing cold and working fine until, suddenly, it wasn't.
I conveyed this to my mechanic friend who checked the system. He said the compressor checked out ok electrically, along with the relays and wiring, and the only obvious cause was the switch itself on the control panel. ...not saying this is gospel, but just repeating what I was told... The underhood 10A fuse for the A/C compressor was blown when he started diagnosing the system, but when changed, it didn't blow again, and it didn't fix anything...

[brcidd]

Blown fuse is a HUGE hint....Does compressor come on when relay is jumpered? That is the place to start...that way yo know if problem is on compressor side of relay, or on control head side of relay.

There is a possibility that the coil fuse blew (if your model compressor has one) It is a thermal overload fuse that detects a slipping clutch and is designed to shut the circuit off before you melt down the pulley bearing and "walk home". You can tell right away if it is "open" by measuring resistance across the coil terminals. I usually do this at the compressor relay so I don't have to crawl under the car or unplug the compressor.

[automan9482]

brcidd: thank you for the follow up, I appreciate it. I don't know if the compressor will come on if jumpered. I admittedly do not know how to do that but I'd be willing to reinstall the control panel and check if I knew exactly how to. My friend checked the compressor relay ("it 'clicked', so it's working") and got under the car, unplugged the compressor and tested the compressor plug with his ohmmeter, and he said it checked out, but I presume he was seeing that power was going to the compressor...

If I may back up a bit on this question, there has been an ongoing problem with the dreaded "clicking HVAC accuators," and the battery randomly dying.
All 3 accuators would continuously chatter when adjusting the temperature on either side, turning on the A/C, adjusting the air flow (defrost to vent, etc.) or switching the fresh air/recirc. That had been going on for a long time, and would occur not only if the engine was running and the system was being used, but also if the car was off and a door was opened, and sometimes when the damn thing was just sitting idle in the driveway and no one was near it. It got to where the owner (this is a friend's car) would just leave everything in one position with the A/C on and would not use the heater or change the air flow to avoid the noise while driving. This is in Florida so he could mostly get away with it...
Then about 1-1/2 years ago, the battery died. It had been replaced 3 years before that, so I figured it was just that time and put a new Interstate battery in. Within a few months it started going dead if the car sat for more than a week or 2, all the while the accuators are clicking away. I thought maybe them running randomly while the car was off was the problem. The owner is on a fixed income and couldn't afford to replace all 3 at $30 - $40 a pop, and I had read they could be disconnected without consequence, so I unplugged them as a stopgap measure. Not a great permanent fix, I know, but the blower and A/C still worked fine, and the clicking noises stopped. The temp. and flow couldn't be adjusted but since that was already the case I figured it didn't matter.
But the battery was still going dead after a week or 2 of sitting. A parasitic draw test on the electrical system showed no obvious drains, so I had the battery replaced under warranty about 4 months ago. It hadn't died since, until after the A/C quit and the car started sitting idle again for more than a week or 2 without being started.

Sorry for the book, but I have no idea if these issues are separate or related, and thought full disclosure would be relevant. With your input, and further online research today, I am thinking more now that the control panel may not be the culprit at all & maybe my friend didn't have it right. But now I am wondering "HVAC control module??" "maybe it IS the compressor?" "or...?"

Thanks again for your input. I have a feeling it is going to point me in the right direction and save me further headache and maybe misspending $.

[brcidd]

Control head failures are rare.....Hardly ever. You can test compressor without control head installed. Simply jump a/c relay socket pins where relay plugs in. Jumper the two big terminal pin plugs- not the smaller ones. Or measure the voltage to ground (with DVM) at each pin plug and find the one big with 12v constant, and jumper it to the one big without 12v constant. Does a/c compressor click on? Ignition need not be on. Do not fiddle with the little pin plugs, they are the relay coil control circuit.

You can also measure resistance to ground from compressor feed at same pin you just jumpered. Should be near 3.5 ohm . if compressor coil is good.

[automan9482]

I followed your advice and jumpered the A/C compressor at the relay base, and here's what I got:
All 4 relay pins/slots are the same size; with the top 2 slots jumpered together I got nothing with the ignition off. With the ignition on the compressor clutch would "click" and engage/disengage but that is all that happened. The clutch would also engage/disengage when jumpered from the top right slot to the bottom left with ignition on.
I measured the voltage in all 4 slots and got 8.3 - 8.4V consistently in the top and bottom left slots, and 0 in the top and bottom right, nothing showed above that. After several attempts in each, I got 0 resistance in all 4 slots.
After checking the voltage and resistance, however, the compressor clutch would only "click" and engage/disengage when jumpered from the top right to the bottom left, but not when jumpered from top right to top left.
I hope the pics help...

[automan9482]

Can someone please offer advice on my next step diagnosing this problem?
I considered starting a new thread, like "A/C failure: control or compressor?" but all the pertinent info is contained in this thread.

*A/C system stopped working suddenly. Control switch would blink when pressed but won't come on. Have been having other issues with this HVAC system I.E. bad accuators, blower fan being picky about coming on if set to low or 2, mystery battery drainage that may/may not be related, but despite that the A/C had worked fine.
*System wouldn't take a charge of R134a, compressor doesn't turn on, refrigerant gauge pegs indicating possible mechanical issues.
*Underhood 10A A/C compressor fuse was blown, fuse was replaced and wiring and relays were checked and deemed good. Was told there is power going to the compressor but the compressor itself wasn't checked to see if it would engage. I was told the control head was the problem.
*Before replacing it I found info stating a new control head would have to be programmed to the BCM, (original reason for starting this thread) and was subsequently advised to check the resistance of the compressor at the relay, and to test if it would come on by jumping the connections at the compressor relay base. My results showed ~8V but no 12V constant, and I wasn't able to get anything for resistance. Exact voltage/resistance results are in my previous reply to this thread.
*The compressor clutch will engage against the compressor pulley when jumpered at the relay, nothing else happens; does that mean it's bad? Or good? With this information, where can I go from here?