2005 Ac runs with Ac switch off

[UltraBoogie]

Hi Ya'll,
I have an interesting problem with my Ac. The compressor runs even with the Ac switch off (as long as the selector is in the defrost or floor/defrost pos). When the climate selector is in the floor pos the compressor shuts off (unless i press the ac switch). I've unplugged the compressor so my mileage isn't suffering. when I switch to defrost my engine still bumps up in rpm and my engine fan pops on. This, in turn, geeks out the shift points and/or keeps the torque converter spun up. In short it's jerky when coming out of any corner(at pretty much any speed) and pulls at the breaks and surges at stop lights.
The ac clutch and compressor are still good, and the ac switch still works(based on turning the ac on/off when in floor selection). What links the climate selector to the ac clutch? Does anyone know of a good AC electrical dia for the 2005 base model?. It might help me make some sense of this. I've seen hints of ECM issues that have similar symptoms on other posts here on gen vibe. I'm really hoping that isn't the case here. Perhaps one of you has had similar issues and come up with a good fix. If you have any questions or need me to try something let me know.

[kumquat]

Hi Ya'll,
I have an interesting problem with my Ac. The compressor runs even with the Ac switch off (as long as the selector is in the defrost or floor/defrost pos). When the climate selector is in the floor pos the compressor shuts off (unless i press the ac switch). I've unplugged the compressor so my mileage isn't suffering. when I switch to defrost my engine still bumps up in rpm and my engine fan pops on. This, in turn, geeks out the shift points and/or keeps the torque converter spun up. In short it's jerky when coming out of any corner(at pretty much any speed) and pulls at the breaks and surges at stop lights.
The ac clutch and compressor are still good, and the ac switch still works(based on turning the ac on/off when in floor selection). What links the climate selector to the ac clutch? Does anyone know of a good AC electrical dia for the 2005 base model?. It might help me make some sense of this. I've seen hints of ECM issues that have similar symptoms on other posts here on gen vibe. I'm really hoping that isn't the case here. Perhaps one of you has had similar issues and come up with a good fix. If you have any questions or need me to try something let me know.

This is normal operation. The compressor is engaged when the selector is in the defrost mode, regardless of whether the AC button is enabled or not. I would guess the engine revs slightly in anticipation of the increased load from the compressor clutch engaging, and when it doesn't engage you get the unnecessary extra power and jerky sensation.

The compressor clutch engagement is controlled by the PCM directly, as opposed to older systems that used electrical components instead of a computer program. An electrical diagram wouldn't do you much good because the clutch would just be plugged into "computer"

Here's GM's description of the compressor operation:

[Nasmfell]

Hi Ya'll,
I have an interesting problem with my Ac. The compressor runs even with the Ac switch off (as long as the selector is in the defrost or floor/defrost pos). When the climate selector is in the floor pos the compressor shuts off (unless i press the ac switch). I've unplugged the compressor so my mileage isn't suffering. when I switch to defrost my engine still bumps up in rpm and my engine fan pops on. This, in turn, geeks out the shift points and/or keeps the torque converter spun up. In short it's jerky when coming out of any corner(at pretty much any speed) and pulls at the breaks and surges at stop lights.
The ac clutch and compressor are still good, and the ac switch still works(based on turning the ac on/off when in floor selection). What links the climate selector to the ac clutch? Does anyone know of a good AC electrical dia for the 2005 base model?. It might help me make some sense of this. I've seen hints of ECM issues that have similar symptoms on other posts here on gen vibe. I'm really hoping that isn't the case here. Perhaps one of you has had similar issues and come up with a good fix. If you have any questions or need me to try something let me know.

As kumquat mentioned, normal. If you live in a colder climate, the compressor engagement helps defrost the windows faster than if it was off, plus it can also pump heat through the cabin faster as well when the heat is selected.

[trb]

Correct. The reason the compressor engages when the defrost setting in selected is to remove the moisture from the air being directed at the windshield. This will speed up the defrosting/ defogging of the windows. I know a few times when the AC in my Mustang was not working, it was a real PITA driving when you can't defog the windows.

[j42.snyder]

There is a mod you can do that's quite simple on the 2003 to 2008's. From what I remember, you just need to get behind the HVAC controls and unplug one connector. I believe it's a single yellow wire that connects in parallel with the A/C button up higher on the dash. Once unplugged, the car will no longer "know" when the dial is turned towards defog, and won't automatically force the A/C on. You can then still choose to run the A/C if desired (for better defogging under some conditions) simply by pressing the A/C button. With this setup, you can safely plug everything else back in under the hood and no longer have any of the driveability issues you've been seeing.

There are probably more detailed directions around. I did a quick search and found the ones I wrote for my 2009 a few years ago, but didn't come across the older ones. If you can figure out how to get behind there, it's pretty simple. I did it on a friend's 2006 about 3 years ago with no issues. I think I just had to pull off the HVAC knobs and maybe undo a couple of screws to get back there. Everything else was snap together. On the 2009-10's, it's similar, but you have to cut a wire rather than just unplugging a connector.

It's funny how some of us "mod" our cars to disable features (or at least gain manual control), rather than add new ones! On mine I've done this mod, added a switch so I can disable the auto headlights on demand (but left on retains normal operation), and figured out how to bypass my TPMS computer with a resistor to keep the irritating light off when my winter rims are installed. The only additions I've done have been a vacuum gauge to help with fuel economy, and trailer hitch/wiring.

Hopefully this helps a bit. Let us know if you try this mod and how it works for you please.

John

[UltraBoogie]

Wow, Thanks for all the help. I ran my dome light all night the other eve. Dropping my battery into the ditch seems to have reset the ECU to a certain extent. the shifting is smoother. Could be coincidence too. j42 posted -
"There is a mod you can do that's quite simple on the 2003 to 2008's. From what I remember, you just need to get behind the HVAC controls and unplug one connector. I believe it's a single yellow wire that connects in parallel with the A/C button up higher on the dash. Once unplugged, the car will no longer "know" when the dial is turned towards defog, and won't automatically force the A/C on. You can then still choose to run the A/C if desired (for better defogging under some conditions) simply by pressing the A/C button. With this setup, you can safely plug everything else back in under the hood and no longer have any of the driveability issues you've been seeing."
Well, that is the way this vibe has worked the last 6ish yrs I've had it. Now its seems to want to work "like it should". That confuses me some. I haven't been into the dash in months (long before the problem) so I don't think that's it. Really this all started after I let my friend use the car for the day. He ran the AC all day and i rarely use it. When I got it back I noticed the compressor clutch still spinning even though the switch wasn't on etc... When i have the chance I'll try that mod.

[kumquat]

So you noticed the system behaving the way it's supposed to, so you started unplugging things..... then your car developed driveability problems as a result....

And instead of putting it back the way it was before, you'll start unplugging more things?

What?

[lannvouivre]

Wow, Thanks for all the help. I ran my dome light all night the other eve. Dropping my battery into the ditch seems to have reset the ECU to a certain extent. the shifting is smoother. Could be coincidence too.

The computer has to have some power from the battery in order to retain its memory, so when the power was exhausted, all the settings were reset. I'm guessing that since it was reset, it's now seen and recorded how the engine needs to run with the compressor no longer engaging.

In relation to you saying that previously you were able to switch to defrost without the compressor engaging: Sometimes my recirculate button would stick, and would remain stuck in "defrost" (which automatically would switch to "fresh air" and release the recirc button). Maybe something was just stuck, and got jarred free? I was actually able to fix the recirc button switch by switching it on and turning the setting to "defrost" over and over.

[joatmon]

So you noticed the system behaving the way it's supposed to, so you started unplugging things..... then your car developed driveability problems as a result....

And instead of putting it back the way it was before, you'll start unplugging more things?

What?

whatchu talkin bout willis?

I believe that you, sir, have misinterpreted the circumstances. If you must find fault, then penalize the OP five yards for improper use of quote tags. The OP asked a question about the auto AC in defrost mode, and was concerned it might be causing idle and shifting issues he was experiencing. Then mentioned accidentally draining the battery via overnight dome light, and now the car is running smoother. (likely from the a resulting ECU reset) A different member identified the connector to unhook to prevent the auto AC in defrost, and the quite odd circumstance that after some time, the auto AC in defrost seems to be back, however this second member hasn't reported driveability problems.

For what it's worth, I disconnected the auto AC in defrost connector from the back of my HVAC controls a long time ago, no problems. vibe owner, a first year genviber, pioneered that here, posting up the first full dash disassembly with lots of pics that has helped many of us for years, and epitomizes the exploratory nature of the early vibe owners.

[kumquat]

So you noticed the system behaving the way it's supposed to, so you started unplugging things..... then your car developed driveability problems as a result....

And instead of putting it back the way it was before, you'll start unplugging more things?

What?

whatchu talkin bout willis?

I believe that you, sir, have misinterpreted the circumstances. If you must find fault, then penalize the OP five yards for improper use of quote tags. The OP asked a question about the auto AC in defrost mode, and was concerned it might be causing idle and shifting issues he was experiencing. Then mentioned accidentally draining the battery via overnight dome light, and now the car is running smoother. (likely from the a resulting ECU reset) A different member identified the connector to unhook to prevent the auto AC in defrost, and the quite odd circumstance that after some time, the auto AC in defrost seems to be back, however this second member hasn't reported driveability problems.

For what it's worth, I disconnected the auto AC in defrost connector from the back of my HVAC controls a long time ago, no problems. vibe owner, a first year genviber, pioneered that here, posting up the first full dash disassembly with lots of pics that has helped many of us for years, and epitomizes the exploratory nature of the early vibe owners.

The way I read it, he noticed the compressor running with the A/C switch off, so he unplugged the compressor. As a result he started experiencing drivability problems.

[joatmon]

sorry, I was set off by the attitude I inferred into your reply.