Question about AC Cars & Trucks

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

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  • 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?

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  • Expert
  • 149 Answers

With thanks to Gary T From TheStraightDope.

Mike,
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

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Posted on Jan 02, 2017

michigan man
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SOURCE: AC blows hot air

try this website fix & troubleshoot heating & A/C www.automedia.com and another car A/C repair www.directgardening.com

Posted on May 25, 2009

dttech
  • 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

emissionwiz
  • 75797 Answers

SOURCE: rough idle on 2004 trailblazer when ac is on

Hello
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

emissionwiz
  • 75797 Answers

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

Hello

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

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