Engine surges with AC/defrost on

2000Durahoe

2000Durahoe

Forum Member
My cousin is having a problem with his Envoy. Over the summer he lost his AC so he just rolled the windows down and kept driving. Now that he's needing his defrost he is noticing the vehicle surges from 600rpm to 350rpm when he puts his windsheild defrost or heat on. If he doesnt put his foot on the gas it dies after about 10 seconds. The voltage drops down to 11.5v or so when it surges. I had him disconnect the ac compressor and now it surges once and goes back to normal. Seems like a bad AC compressor to me...right? I still don't get the one inital surge though. Maybe he needs some seafoam or something?

I talked to my brother about it and he said he thinks the AC compressor might help out in some way when the temp is above freezing. At least thats what he HEARD from a guy at work.
 
the a/c runs while in defrost to dry the air.
the throttle body opens when the a/c clutch command is sent to keep idle even.
get the a/c issue fixed
 
2000Durahoe said:
My cousin is having a problem with his Envoy. Over the summer he lost his AC so he just rolled the windows down and kept driving. Now that he's needing his defrost he is noticing the vehicle surges from 600rpm to 350rpm when he puts his windsheild defrost or heat on. If he doesnt put his foot on the gas it dies after about 10 seconds. The voltage drops down to 11.5v or so when it surges. I had him disconnect the ac compressor and now it surges once and goes back to normal. Seems like a bad AC compressor to me...right? I still don't get the one inital surge though. Maybe he needs some seafoam or something?

I talked to my brother about it and he said he thinks the AC compressor might help out in some way when the temp is above freezing. At least thats what he HEARD from a guy at work.
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Have the charging system checked out. Low voltage and bad batterys and alternators can cuase idle issues.
 
1BADAIR said:
the a/c runs while in defrost to dry the air.
the throttle body opens when the a/c clutch command is sent to keep idle even.
get the a/c issue fixed
Click to expand...

Could it be an IAC issue then? Meaning start off by cleaning the TB and IAC?

Sean said:
Have the charging system checked out. Low voltage and bad batterys and alternators can cuase idle issues.
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Both are new actually. The alternator went on it and less than a week later the battery did. Them might be 3 months old.
 
2000Durahoe said:
Could it be an IAC issue then? Meaning start off by cleaning the TB and IAC?



Both are new actually. The alternator went on it and less than a week later the battery did. Them might be 3 months old.
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electronic TB doesn't have a IAC.
the low voltage is probably from the idle going to 350rpm
does the idle go up or down when the a/c is unplugged?
 
1BADAIR said:
electronic TB doesn't have a IAC.
the low voltage is probably from the idle going to 350rpm
does the idle go up or down when the a/c is unplugged?
Click to expand...

Sorry, didn't know it was drive by wire. I idle isn't effected more than a few rpm's with the AC/defrost on or off. The surge is the only effect of the RPMs. With the AC/defrost on it idles at 600 and with it off it maybe idles at 625rpm. To me that seems normal.
 
1BADAIR said:
electronic TB doesn't have a IAC.
the low voltage is probably from the idle going to 350rpm
does the idle go up or down when the a/c is unplugged?
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a drop to 12.5 volts would be tolerable. However 11.5 is cuase for concern. Also with the responsiveness of factory guages the indicator most likely responds after the idle drop.

The only other low idel cuases that TB related could be a dirty throttle plate. But usually they stick.
 
2000Durahoe said:
Sorry, didn't know it was drive by wire. I idle isn't effected more than a few rpm's with the AC/defrost on or off. The surge is the only effect of the RPMs. With the AC/defrost on it idles at 600 and with it off it maybe idles at 625rpm. To me that seems normal.
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This indicates a high electrical load cuasing idle instability. Check that alternator. the Compressor Clutch can pull upto 30 amps.
 
I'll have him check it tomorrow when he goes out. Thanks Sean.

Actually, thinking about it. Can a place like Autozone check it while its on the car? I know they have that machine to test them inside. Also, can they test the battery while in the car?
 
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Most shops have a VAT machine, that can test the battery, alternator & starter while in the car. We charge $20 to do these test's, sometimes we do it for free. It may be worth the little bit of money to get you in the right direction
 
Well I looked yesterday. I don't know why he said 11.5v. It's maybe dropping to 12.5-12.6v. Apparently a gauge with only 3 numbers is hard for some people to understand. :shutup: Still haven't got it tested though. He'll need to find a shop that can test it on the the car. For now, its working alright with the AC compressor unplugged.
 
2000Durahoe said:
Well I looked yesterday. I don't know why he said 11.5v. It's maybe dropping to 12.5-12.6v. Apparently a gauge with only 3 numbers is hard for some people to understand. :shutup: Still haven't got it tested though. He'll need to find a shop that can test it on the the car. For now, its working alright with the AC compressor unplugged.
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the only other things I can think of that could cuase such a big drop on a AC start is

to much oil in the AC system and or a bound up and overcharged compressor.

Also there is a AC high side pressure transducer. That is if did not read properly could cuase a low idle.

the job of the pressure sensor is to relay back to the PCM information on High side line pressure so that the ECM can predict additional airflow to adjust throttle position to maintain a constant idle speed.

I would think the adaptives should have adapted and fixed this issue by now.

One last parting thought.

Did you guys check for vacum leks and any fuel trim data looking wierd. Some of the truck intakes have had problems with gaskets fialing on the corner cylinders.
 
Sean said:
the only other things I can think of that could cuase such a big drop on a AC start is

to much oil in the AC system and or a bound up and overcharged compressor.

Also there is a AC high side pressure transducer. That is if did not read properly could cuase a low idle.

the job of the pressure sensor is to relay back to the PCM information on High side line pressure so that the ECM can predict additional airflow to adjust throttle position to maintain a constant idle speed.

I would think the adaptives should have adapted and fixed this issue by now.

One last parting thought.

Did you guys check for vacum leks and any fuel trim data looking wierd. Some of the truck intakes have had problems with gaskets fialing on the corner cylinders.
Click to expand...

I'm still leaning towards failed compressor. I very highly doubt it would be overcharged or too much oil. The system has never been touched since General Motors.

I haven't checked for vacuum leaks but wouldn't there be other issues than just a surge of RPM when the AC/defrost is on? The car is still getting 17.5mpg according to the display in the dash. Also, its not leaking or burning coolant or oil like you'd get with a gasket.
 
2000Durahoe said:
I'm still leaning towards failed compressor. I very highly doubt it would be overcharged or too much oil. The system has never been touched since General Motors.

I haven't checked for vacuum leaks but wouldn't there be other issues than just a surge of RPM when the AC/defrost is on? The car is still getting 17.5mpg according to the display in the dash. Also, its not leaking or burning coolant or oil like you'd get with a gasket.
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I don't know the service history. I was giving you a few things to look at. If you acess to a scan tool checking those pressure values against a known good guage set might be worth looking at.

A vaccum leak might only show up at high idle loads. At least with as good as the adaptive control on the late model vehicles are.

Just sharing a few ideas.

First step. Do some testing, gather data, evaluate data. Form conclusion from data.
 
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