Question about 2003 Chevrolet TrailBlazer

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Engine almost stalling when ac is turned on

Ac compressor kicks on/off at regular intervals (approx. 8 sec.) This causes the engine rpm to drop to about 300 (sometimes stalling the engine) and then it attempts to recover, spiking to about 1300. Each time the engine drops to 300 RPM the AC compressor kicks on for just a moment and then kicks right back out.

Additionally, the dashboard air vents quit discharging air at the same time this problem started. Air will come out on windshield and floor but not at dashboard vents. Not sure if this is related to the above problem but both started at same time.

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You may have a faulyt IAC sensor not idling up enging when a/c is on

Posted on Jul 22, 2009


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When i turn on my heat/air on defrost or auto my rpms go up... what could cause this

The basic concept is that in auto or defrost the air conditioner compressor is activated.
The compressor when activated via an electrical clutch adds an additional load that will reduce the engine RPM. The the RPM is increased slightly when the A/C is activated to prevent the engine from stalling. Power produced by the engine is increased by allowing more air and gas into the engine. When it is working perfectly the RPM will remain the same but the engine will produce the additional power to power the AC compressor.

Usually the bi-pass air valve is how the compensation for the additional power is accomplished.

Depending on your make year and model several methods to achieve the AC compensations have been used. In your specific case if the compressor is not working(no Air) and the compensation is open loop no engine control electronics I would expect a surge in RPM. With no additional load from the AC the additional air into the engine would increase the RPM.
26106712-qb20k32l4fvb2dr3l0mnapaf-4-0.jpg On older cars there is a solenoid that has an adjustment for idle speed when the solenoid is activated. See the image above.
Hope this helps?

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98 mitsubishi chariot grandis gdi, making funny buzzing noise then engine stalls

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Starting at about 20 MPH I get a low rythmetic rumble about every 15 to 20 sec. apart that not only drops the rpm by about 50 but also makes the MPG gauge dip a bit also. This stops if I am going 70 or...

The only thing I can think of that would happen at time intervals that far apart is the air conditioning compressor kicking on and off. The idle air control is supposed to compensate for this to keep the RPM steady, but if you have an air leak in the intake tubing, or dirt in the air valve, I can imagine that it might be more noticeable. My theory would be consistent with the fact that you don't notice it at highway speed when the engine is pulling harder and running faster. I would not worry too much about it.

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2003 Honda CR-V when the A/c compressor kicks on the engine drops 300 rpm, like it's going to stall. It's making a clunk noise when kicking on and I changed the battery thinking it was weak.

sounds like it's the iacv or idle air control valve not working due to dirt in the orifice or the iacv is burnt out and cannot turn correctly, or the wiring to it is faulty.

Good luck on the repair.

If the A/C compressor makes a clunk noise when kicking on, that could indicate a worn out compressor.

You're right, 300 rpm is way too low. It should be closer to 600 or 700 or 800 rpm and remain smooth when the a/c compressor kicks on.

Nov 07, 2010 | 2002 Honda CR-V

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Trying to confirm if A/C compressor bad. When A/C

Before anything is done to the AC, have the throttle body cleaned. A dirty throttle body will cause engine RPM to drop or even stall.
What makes you think the compressor is seized? Does the compressor pulley spin when AC is engaged? If compressor was seized the pulley would not move and belt would squeal.

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2002 Santa Fe 2.7 V6 (California Car) 260,000 + miles. Engine idle will increase to about 1500 RPM and drop back to normal without notice, at times difficult to start (must hold throttle about half open)...

I faulty Idle Air Control valve (IAC) can cause these specific symptoms. You could try diconnecting the IAC valve (usually near the throttle body) and regulating the idle yourself. If the fluctuations go away and you are able to hold a constant idle position with the gas pedal (if vehicle will start), the IAC is the problem.

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Engine seems to lack power w/ ac on . now engine will stall

Check the RPM if it drops when you have the AC on while the car is not moving. If it does drop you may want to check on the idle compensator. Its job is to bring increase RPM to make up for the added load. You may also want to check on the idle if it is below the normal speed. The added load may decrease the speed and send you to stall. If they all check out OK, you may want to check out the compressor as well if it gives the engine too much load. This can be caused by a faulty compressor or too much freon, or the bearing may be bad (with the bearing, you will get to hear a screeching or whinning sound).

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Fuel system

Car is not seeing rpm's. Sounds like a bad crank sensor. The rpms signal the pump to turn on while the vehicle is running.

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