My 93 Sidekick overheats whenever running the AC. Whenever i turn it on the rpms drop to 500 should it not pick up a little when i turn it on, or is anyone else having this problem? The condensor fan is working also i check it yesterday.

Yes, the engine RPMs should rise a little, when you turn the AC on.  Is it actually overheating (either boiling over and/or the needle is running into the red on the gauge)?  When I turn my AC on, and am driving at slow speeds or idling, the temp gauge will rise a little higher than normal....but it has never actually overheated.

It started to boil over yesterday before i realized the needle was almost in the red. What could be the problem for it not idling up when the AC is on? I thought the slow fan speed from engine idling so low could have something to do with it.

I don't remember offhand what controls the idle up when the AC is turned on.....there might be a sensor, or it could be in the ECM itself.  If I have time, and remember, I'll check later on and post back.

I had trouble with my '01 when turning on the A/C - RPMs would drop.  It happened when turning on the headlights and HVAC fan too.  Turned out to be the IACV (idle air control valve).  It was two minutes to swap out on mine.

The extra electrical load from these components requires the alternator to increase the output from its normal operation.  This means extra load on the motor which requires extra fuel.  The IACV senses this extra load and tells the ECU to add more fuel which keeps the idle normal.

I have no idea how the '93 works but I'd guess it is similar. The IACV is a somewhat common replacement item on many fuel injected vehicles.

Sometimes the IACV is also called a Stepper Motor.

If you unplug the electrical connector from an IACV and start the car the idle should be very high (like 1500-2000 rpm).  As you turn on things like A/C, fans, rear defroster, and headlights you'll see the idle come down.  The amount of fuel going to the motor is actually the same but the added load from the alternator is dragging the motor down and it now has no way to compensate for it.  The high idle that occurs from unplugging it can be a benefit if your IACV breaks because it can help get you home without the engine bogging down.

That's a good explanation Frank84, mine also drops rpm ( not always, but sometimes) if I switch on the AC, and I've also had the occasional overheating issue when running the AC., I'm going to have to check the IACV. Thanks!

Thanks Skyhiranger and Frank84 for your responses i will check that as soon as i get a chance Frank84. The only time mine idles down is when i turn the AC on. The lights or fan motor does not effect the idle, i checked that a little while ago, but it makes sense after you mentioned it.

I hope thats not whats wrong with it Frank84, i just looked it up on autozones website $325 , so if it is that it probably wont get fixed and i will not be running the AC.

I hope thats not whats wrong with it Frank84, i just looked it up on autozones website $325 , so if it is that it probably wont get fixed and i will not be running the AC.

I have some good used ones for sale, if you find out that is what is wrong.

I had trouble with my '01 when turning on the A/C - RPMs would drop.  It happened when turning on the headlights and HVAC fan too.  Turned out to be the IACV (idle air control valve).  It was two minutes to swap out on mine.

The extra electrical load from these components requires the alternator to increase the output from its normal operation.  This means extra load on the motor which requires extra fuel.  The IACV senses this extra load and tells the ECU to add more fuel which keeps the idle normal.

I have no idea how the '93 works but I'd guess it is similar. The IACV is a somewhat common replacement item on many fuel injected vehicles.

Sometimes the IACV is also called a Stepper Motor.

If you unplug the electrical connector from an IACV and start the car the idle should be very high (like 1500-2000 rpm).  As you turn on things like A/C, fans, rear defroster, and headlights you'll see the idle come down.  The amount of fuel going to the motor is actually the same but the added load from the alternator is dragging the motor down and it now has no way to compensate for it.  The high idle that occurs from unplugging it can be a benefit if your IACV breaks because it can help get you home without the engine bogging down.

Actually the IAC valve does not sense anything - the ECU has inputs wired to the electrical circuits and knows what additional loads are present through those inputs and then instructs the IAC to allow more air to compensate for the additional load, the ECU also adds fuel as required based on the feedback from the O2 sensor.

Some IAC valves are stepper motor controlled - as in an '01, others are not, as in the OP's '93

On an 01, the ECU controls the a/c and idle up is handled through the IAC - however I believe the 93 is different - as far as I know there is a separate AC amplifier and there is no direct connection to the ECU - unfortunately I do not have the a/c diagrams for the vehicle to hand, and so cannot be 100% certain, but I believe the a/c idle up is handled by a separate VSV air bleed - I will try to track down the necessary drawings and let you know.

Edit

I found A/C drawings for a 91 & 95 - both of them have a direct connection between the a/c amplifier and the ECU, presumably the 93 does also

You may want to check the fan clutch also

Wild

You may want to check the fan clutch also

Wild

I checked it a few weeks ago when i started using the AC. The only time it does it is when im in stop and go traffic with it on, when its on  the rpm needle drops from 8-900 rpms down almost to the pin that it rest on when its shut off. Ive never seen one idle so low, you can almost count the blades on the fan and the turns of the motor with the AC on.

Quote from: Frank84 on July 08, 2010, 02:06:38 PM

I had trouble with my '01 when turning on the A/C - RPMs would drop.  It happened when turning on the headlights and HVAC fan too.  Turned out to be the IACV (idle air control valve).  It was two minutes to swap out on mine.

The extra electrical load from these components requires the alternator to increase the output from its normal operation.  This means extra load on the motor which requires extra fuel.  The IACV senses this extra load and tells the ECU to add more fuel which keeps the idle normal.

I have no idea how the '93 works but I'd guess it is similar. The IACV is a somewhat common replacement item on many fuel injected vehicles.

Sometimes the IACV is also called a Stepper Motor.

If you unplug the electrical connector from an IACV and start the car the idle should be very high (like 1500-2000 rpm).  As you turn on things like A/C, fans, rear defroster, and headlights you'll see the idle come down.  The amount of fuel going to the motor is actually the same but the added load from the alternator is dragging the motor down and it now has no way to compensate for it.  The high idle that occurs from unplugging it can be a benefit if your IACV breaks because it can help get you home without the engine bogging down.

Actually the IAC valve does not sense anything - the ECU has inputs wired to the electrical circuits and knows what additional loads are present through those inputs and then instructs the IAC to allow more air to compensate for the additional load, the ECU also adds fuel as required based on the feedback from the O2 sensor.

Some IAC valves are stepper motor controlled - as in an '01, others are not, as in the OP's '93

On an 01, the ECU controls the a/c and idle up is handled through the IAC - however I believe the 93 is different - as far as I know there is a separate AC amplifier and there is no direct connection to the ECU - unfortunately I do not have the a/c diagrams for the vehicle to hand, and so cannot be 100% certain, but I believe the a/c idle up is handled by a separate VSV air bleed - I will try to track down the necessary drawings and let you know.

Edit

I found A/C drawings for a 91 & 95 - both of them have a direct connection between the a/c amplifier and the ECU, presumably the 93 does also

So it could possibly be the ECU?

So it could possibly be the ECU?

It's unlikely to be the ECU - it's not impossible, but in my opinion, unlikely.

I think power steering was optional on the '93 - does yours have it?  What happens if you turn to full lock and hold the wheel there - what should happen is as the P/S pump loads the engine, a switch on the pump let's the ECU know and the ECU should compensate by bring ing the idle up.

There should be an idle up arrangement for the following items - lights, blower fan, p/s pump, rear screen defrost, and a/c - if it works for at least one of them, I'd say you can rule out the ECU and IAC valve.

So far it hasn't idled up when turning anything you mentioned on, but turning on any of those doesn't seem to drag it down either. I will try the power steering when i get off work.

Well if it's getting hot while sitting and idling in traffic, rev the engine
and listen for the fan, you should hear it making a whirring noise, if not
then it's not working correctly, and could cause of your problem, the
low idle also isn't helping, so you could rev the engine a little when sitting
to like 1000-1200 RPM and see if it helps

Wild