Question about AC Cars & Trucks

1 Answer

Turn on ac or defrost and it dies has a rough idle

Posted by on

  • Ryan Lutton
    Ryan Lutton Apr 21, 2015

    Hi Mike Potarf, I want to help you with your question, but I need more information from you. Can you please add details in the comment box? What vehicle, is this a Trailblazer by chance?



1 Answer

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that gotĀ 5 achievements.


    An expert whose answer gotĀ voted for 20 times.


    An expert who has written 20 answers of more than 400 characters.

  • Expert
  • 154 Answers

With thanks to Gary T From TheStraightDope.

it looks like your battery is knackered. Test it by following Gary's procedures below or perhaps just buy a new one.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
If it's a serviceable battery, remove the vent caps and test the specific gravity of the electrolyte fluid. A tester for this is pretty inexpensive ($5-10?). A difference of 30 points between any cells is suspect, a difference of 50 is bad (replace now). If there's not enough liquid in the cells to fill the tester, bring them up to their full mark with clean water and wait a day or two for it to mix in. If the liquid is below the metal plates inside, buy a new battery now.

Other tests require pricier equipment or trickier procedures. A load test can be done with a load tester, or by disabling something to prevent the engine starting and then cranking it for 10 seconds, in either case reading the battery voltage at the point it's been under load for 10 seconds. Starting with a fully charged battery (12.6 v), it should read at least 9.8 v for the load test - but if it's close to that, it's weak. Really good batteries read over 11 v.

Posted on Apr 21, 2015


6 Suggested Answers

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017

michigan man
  • 3533 Answers

SOURCE: AC blows hot air

try this website fix & troubleshoot heating & A/C and another car A/C repair

Posted on May 25, 2009

  • 4803 Answers

SOURCE: rpms drop when defrost or ac is on

Then you need to scan your onboard computer network. Your A/C compressor is controlled by your Powertrain Control Module (PCM) and the HVAC Control unit controlls the rest of your HVAC system and communicates with the PCM when A/C requests are made. Apparently, somebody is either not getting the message or the PCM is unable to control the throttle like it is supposed to.

Posted on May 27, 2012

  • 80608 Answers

SOURCE: rough idle on 2004 trailblazer when ac is on

The engine and transmission in this cars drive train are fully electronically controlled by a computer called the PCM (Power Train Control Module). Whenever a problem like this occurs the computer stores a record of the problem (there are of course some exceptions to this, like the fuel pump for instance) in the form of a fault code in its memory, to read these fault codes you must have the systems memory scanned with a special tool. Once the fault code(s) are read you then must perform the appropriate diagnostic testing to find and resolve the problem(s) DO NOT REPLACE ANY PARTS UNTIL THE DIAGNOSIS & TESTING IS COMPLETED.

Posted on Jul 08, 2012

  • 80608 Answers

SOURCE: rough-idle-when-ac-is-turn-on


The engine and the automatic transmission in this vehicle are computer controlled and in most cases when a fault occurs a fault code is stored in the memory of the computer control module. There are exception to this, such as the Mass Airflow Meter and fuel pressure problems. What must be done is to have all the basic testing done such as a scan of the system for fault codes as well as a check with a live data scanner tool for engine functions that are not within range of normal, a trained technician is required to know what is correct and what isn't, then based on careful diagnostics done from a factory repair manual the correct part is replaced or the wiring repaired or the computer replaced (known as the PCM), which is very rarely the problem. Other basic checks must be done as well such as mechanical problems with the engine as well as engine state of tune and mileage on the engine. The transmission can have mechanical issues as well such as no gear engagement at all or a filed pump or other pressure related problems.

Posted on Sep 14, 2012

  • 253 Answers

SOURCE: Finding the idle goes up n down/die out when using Defrost

Sounds like a vacuum problem. Do you have a seemingly hard brake pedal? If you do chances are your brake booster is leaking vacuum. If not check your vacuum lines. Your heater system is controlled by vacuum.

Posted on Feb 22, 2013

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Idles rough multiple codes

Hello Amy, not a POS, just has quirks like all vehicles do. It's a very good engine. I'm going to address the bad idle which is very common after the battery was disconnected for any reason. This is a job that you can do yourself for around $8. Remove fuses # 10 and # 28 under the hood, then remove the throttle body and clean both sides with a sensor safe spray like Seafoam. It's just 4 bolts and a electrical connector that it. This will solve your rough idle when every your AC or Defroster are on. The other lights, do they go off if you turn the car off and restart with the steering wheel pointing straight?

Nov 25, 2017 | 2002 Oldsmobile Bravada

1 Answer

Car stalls when ac or defrost on

Sounds like the compressor is dragging the engine down. The compressor runs in ac and defrost mode. You might try unplugging the compressor to verify.

Jul 21, 2013 | Ford Cars & Trucks

1 Answer

Idle air control valve

should be right on or very near the throttle body.

Jan 20, 2013 | 2002 GMC Envoy

2 Answers

My blazer motor dies out when I turn on the ac or defrost.Why?Also the passenger side headlight goes out If I wiggle the socket It comes back on for awhile.

Replace the headlight pigtail or plug and the headlight also. Engine is idleing too low probabally IAC (idle air control motor) is worn out. Also there is a sensor when you turn on a/c witch also comes on with the defroster that tells the pcm to adjust idle for a/c operation that may be bad or not connected.

Nov 16, 2010 | 2004 Chevrolet TrailBlazer

3 Answers

Rough Idle when cold runs seems to run ok hot but still almost stalls when you turn on AC and you are at a stop also noticed that the volt meter reads 9v with the AC and the lights on with the AC and...

mcdevito75 here, Sounds like a faulty voltage regulator, it"s 1 unit with the alternator, change the alternator, also the alt. supplies juice to the ignition switch, distributor abd plugs, thus a rough idle due to bad alternator.

Jun 19, 2010 | 1994 GMC Suburban

1 Answer

Kia idles rough when switching from heat to defrost also happens sometimes when driving

That's your AC compressor kicking in and out to assist in defrosting. AIS (automatic idle speed motor) should overcome that, unless it needs cleaning, or maybe a tune-up is due., I'd try cleaning throttle body with spray cleaner first to see if that in itself may help. Spray a little extra in direction of port for AIS motor.

Dec 24, 2009 | 2003 Kia Spectra

2 Answers

Engine stalls

Assuming you have the correct size battery, this really shouldn't happen! I am assuming the engine is idling at fairly low RPMs, so when the AC kicks on, it kills the engine? It might be that you need to drive the car for a bit so that the engine computer can "relearn" your settings, which disappear when you change the battery. Or, when your battery died, one of your sensors might have gone with it. There is a idle sensor on most cars that raises the idle RPMs when the AC comes on.

Aug 30, 2009 | 2004 Chevrolet TrailBlazer

1 Answer

AC blows hot air

try this website fix & troubleshoot heating & A/C and another car A/C repair

May 25, 2009 | 2002 GMC Envoy XL

1 Answer

Rough idle when a/c on

it is normal for your car to idle down when the ac pump cuts in just have your timing checked and adjust your idle as necessary at about 750 rps at normal idle with ac off also just make sure they havent overtightened the ac belt and pulley.

Jun 04, 2008 | 1994 Honda Accord

Not finding what you are looking for?
Cars & Trucks Logo

Related Topics:

23 people viewed this question

Ask a Question

Usually answered in minutes!

Top AC Experts

old marine
old marine

Level 3 Expert

2153 Answers


Level 3 Expert

450 Answers

David Harrelson
David Harrelson

Level 3 Expert

5438 Answers

Are you an AC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides