Strange AC issue
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
Strange AC issue
Drive the Z today after sitting for about 2 months. The AC would switch off at idle, but a slight rev and it would kick in as long as I keep it above idle. I sat in the driveway with the RPM at 1000 and it blew nice cold air, but shut off as soon as it dropped back to 800-850 idle. It doesnt just stop blowing cold (does that too), but the light on the panel goes out as well.
2002 Z06, ~50k miles, usually driven about once a week. Mods are a mild cam, full exhaust and CAI. All mods have been on for a while with no issues until today. Couldnt find what I was looking for in the search so im hoping someone can shed some light on this. I have not checked for codes yet. Ill try and get to that in the morning.
2002 Z06, ~50k miles, usually driven about once a week. Mods are a mild cam, full exhaust and CAI. All mods have been on for a while with no issues until today. Couldnt find what I was looking for in the search so im hoping someone can shed some light on this. I have not checked for codes yet. Ill try and get to that in the morning.
Drifting
Joined: May 2008
Posts: 1,695
Likes: 490
From: Denver, NC
Was the battery low from sitting 2 months? Did you check the battery voltage at idle when this was occurring? Just starting with the basics. You description sounds like the alternator had to get the power up for the AC to operate - the clutch coil needs juice to engage and stay engaged.
Last edited by Ed Ramberger; Jul 15, 2019 at 09:42 PM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,595
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From: Cape Coral, Florida
It sounds like you may need a “recharge” of the refrigerant...PCM is looking for a certain pressure via a pressure “sensor” and not a switch...putting it in simple terms and if it doesn’t see it...”no workie”...LOL !!!...Revving the engine increases that pressure !!...don’t do that DIY recharge thing...take it to a pro that has the right equipment and knowledge !!
Last edited by C5 Diag; Jul 15, 2019 at 10:13 PM.
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
Was the battery low from sitting 2 months? Did you check the battery voltage at idle when this was occurring? Just starting with the basics. You description sounds like the alternator had to get the power up for the AC to operate - the clutch coil needs juice to engage and stay engaged.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,595
Likes: 4,055
From: Cape Coral, Florida
Ed, no problem...you probably just had a brain fart...I get them quite frequently these days...LOL !!
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
It sounds like you may need a “recharge” of the refrigerant...PCM is looking for a certain pressure via a pressure “sensor” and not a switch...putting it in simple terms and if it doesn’t see it...”no workie”...LOL !!!...Revving the engine increases that pressure !!...don’t do that DIY recharge thing...take it to a pro that has the right equipment and knowledge !!
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Burning Brakes
Joined: Oct 2016
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From: Massillon Ohio
It is either a low pressure issue or a tuning issue.
Have the a/c tested first.. That will be a quick idea of why it isn't working. If the test comes back good and it is not low on pressure, then your tuner will need to adjust some tables in the computer to make it work. I doubt the cam is large enough in your car to mess with the idle though, but it is possible.
Have the a/c tested first.. That will be a quick idea of why it isn't working. If the test comes back good and it is not low on pressure, then your tuner will need to adjust some tables in the computer to make it work. I doubt the cam is large enough in your car to mess with the idle though, but it is possible.
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
It is either a low pressure issue or a tuning issue.
Have the a/c tested first.. That will be a quick idea of why it isn't working. If the test comes back good and it is not low on pressure, then your tuner will need to adjust some tables in the computer to make it work. I doubt the cam is large enough in your car to mess with the idle though, but it is possible.
Have the a/c tested first.. That will be a quick idea of why it isn't working. If the test comes back good and it is not low on pressure, then your tuner will need to adjust some tables in the computer to make it work. I doubt the cam is large enough in your car to mess with the idle though, but it is possible.
Burning Brakes
Joined: Oct 2016
Posts: 1,209
Likes: 363
From: Massillon Ohio
Le Mans Master
Joined: Apr 2012
Posts: 7,814
Likes: 2,266
From: Brighton MI
OP - are you saying that the compressor kicks-off at idle - then kicks-on once you raise the revs a bit?
If so, it is NOT a pressure issue. The only way to raise pressure in the system (on the high side) or lower it (on the low side) is for the compressor to be running. Simply bumping the engine revs (with the compressor not running) does NOTHING to increase/decrease pressure in the a/c system.
If so, it is NOT a pressure issue. The only way to raise pressure in the system (on the high side) or lower it (on the low side) is for the compressor to be running. Simply bumping the engine revs (with the compressor not running) does NOTHING to increase/decrease pressure in the a/c system.
Drifting
Joined: May 2008
Posts: 1,695
Likes: 490
From: Denver, NC
OP - are you saying that the compressor kicks-off at idle - then kicks-on once you raise the revs a bit?
If so, it is NOT a pressure issue. The only way to raise pressure in the system (on the high side) or lower it (on the low side) is for the compressor to be running. Simply bumping the engine revs (with the compressor not running) does NOTHING to increase/decrease pressure in the a/c system.
If so, it is NOT a pressure issue. The only way to raise pressure in the system (on the high side) or lower it (on the low side) is for the compressor to be running. Simply bumping the engine revs (with the compressor not running) does NOTHING to increase/decrease pressure in the a/c system.
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
OP - are you saying that the compressor kicks-off at idle - then kicks-on once you raise the revs a bit?
If so, it is NOT a pressure issue. The only way to raise pressure in the system (on the high side) or lower it (on the low side) is for the compressor to be running. Simply bumping the engine revs (with the compressor not running) does NOTHING to increase/decrease pressure in the a/c system.
If so, it is NOT a pressure issue. The only way to raise pressure in the system (on the high side) or lower it (on the low side) is for the compressor to be running. Simply bumping the engine revs (with the compressor not running) does NOTHING to increase/decrease pressure in the a/c system.
I hope to trouble shot a bit this afternoon and I'll report back. I'll check battery and codes first. Then I'll check pressure just to see what it's at. If I can't narrow it down there then it's likely of to a pro.
Le Mans Master
Joined: Apr 2012
Posts: 7,814
Likes: 2,266
From: Brighton MI
I tend to agree with Ed here, at least as a place to start. If the battery is low, it is possible that at idle there isn't enough voltage to engage the compressor clutch. Once you bump the revs a little, the alternator output goes up and might be bringing system voltage up just enough so that the compressor engages. Said another way, the a/c system is trying to engage the compressor at idle, but it won't engage due to insufficient available voltage...bumping the revs increases available voltage due to higher alternator output.
I would check system voltage at idle then again at slightly higher rpm (when compressor engages) and see if there is any significant difference (increase) in system voltage.
I would check system voltage at idle then again at slightly higher rpm (when compressor engages) and see if there is any significant difference (increase) in system voltage.
Last edited by 4XLR8N; Jul 18, 2019 at 09:09 AM.
Burning Brakes
Joined: Oct 2014
Posts: 874
Likes: 107
From: Detroit MI
This is tuning, I'd almost bet on it. I had the exact same problem with my car when I installed the cam and had it tuned
https://www.corvetteforum.com/forums...m-stumped.html
That fixed it for me.
https://www.corvetteforum.com/forums...m-stumped.html
That fixed it for me.
Thread Starter
Melting Slicks
Joined: Oct 2006
Posts: 2,193
Likes: 156
From: Navarre FL
This is tuning, I'd almost bet on it. I had the exact same problem with my car when I installed the cam and had it tuned
https://www.corvetteforum.com/forums...m-stumped.html
That fixed it for me.
https://www.corvetteforum.com/forums...m-stumped.html
That fixed it for me.
If it's not the voltage or the pressure I can check with my tuner.
Melting Slicks
Joined: Jan 2009
Posts: 3,275
Likes: 739
From: Miami FL
You will need an A/C Manifold Gauges set. Doesn't have to be top-of-the-line and uber expensive. One from Harbor Freight would be fine, or get a free loaner from an auto parts store.
Although not essential, a Thermometer will give you a better idea of the A/C system health. You can get for around 5 bucks:
Pressures vary not only with the RPMs of the engine, as mentioned above, but with humidity and temperature. Don't add refrigerant blindly.
Check both pressures to have an idea of how things are. Take a look at this Post. It has detailed instructions to check/add refrigerant.
-These are the CliffsNotes:
Find the current ambient temperature and humidity. Then, using the chart below, determine your target values for:
- High Pressure
- Low Pressure and
- Center Vent Temp.
Then take your readings. Make sure you take them with (otherwise readings will be affected):
- Engine @ 2000 rpm
- A/C in coldest setting
- Fan at maximum speed
- Both windows down
- Thermometer in center air vent
When adding refrigerant, pay attention to both pressures, otherwise you might end up with the high side sky-high trying to get the low side to the chart's value.
Let us know your findings
Last edited by GCG; Jul 18, 2019 at 11:40 AM.