e-man

Hey guys. I'll explain in more detail below, but the question is simple. I think we all have the low idle problem. With the a/c off at a stoplight in drive, the car idles at around 400 and shakes a bit. Turn the a/c on (or the headlights, for that matter) and the RPMs kick up to 650 and the car stops shaking. So, my question is what component of the a/c system draws power to cause the RPMs to go up?

Here's the problem I'm having. I've owned the car (99 GS4) for 5 years. I drive with the climate control on Auto year round. Whenever the temperature outside is above 32 degrees, with the climate control on auto, the car idles at around 650 RPM, in drive, while stopped at a stoplight. When the temperature outside dips below 32 degrees, even with the climate control on auto, the RPMs dip to around 400 and the car shakes. I'm totally fine with it and have written it off to normal behavior. I always assumed that when the temperature outside dips below 32 degrees, the compressor turns off and causes the engine to idle low. I've observed this consistently for the last 5 years, that is until about 2 weeks ago.

About 2 weeks ago, my a/c went out on me. The dealer said it was low on freon, so they charged it. Now, the a/c system is behaving differently than it did before it was charged. Like I said above, whenever it was above 32 degrees outside, I never had the low idle problem unless I turned off the climate control. Now, there seems to be something in the a/c system that is kicking on and off that's giving me low idle even when it's 60+ degrees outside.

I know many will say it's the compressor kicking on and off, and maybe that's the case, but that doesn't explain why I never had this issue for the past 5 years unless the outside temperature dipped below 32 degrees.

Any thoughts/comments would be greatly appreciated. Thanks.

e

BCP43002

I think it would be the electric fans kicking on.

e-man

I was thinking that could be one of the things. But here's the question. If I never had low idle before with the climate control on, does that mean that the fans never turned off before and for some reason now, only after getting a freon recharge, are the fans starting to turn on and off?

BCP43002

If you took it off of auto, and then turned on the A/C, do you hear a click that means the clutch has kicked in and are the fans on? The idle speed for a 430 with the clutch off is around 750rpm, clutch on is around 800rpm. I don't know a 400 rpm's. Did you look at your sight glass to see what it looks like? There should be a few bubbles flowing outward.

e-man

If I turn off auto and force the a/c on (by lowering the set temperature), it blows ice cold, so I assume that means the compressor is on. Even under that scenario, I sometimes get the low idle problem.

What is the sight glass?

GS300-2002

you can see if the compressor is on by looking at the a/c light in the top right or passenger side
also in my car if i am idling in park i know that when i turn the a/c on the revs jump up 200 rpm and you can actually hear the difference in throttle through the exhaust. But i dont have the low idle problem like you do and i have the drive by wire system whereas you have the cable

BCP43002

The sight glass is a small window on your receiver that you look through to check your freon. Your A/c lines are hooked up to it. Do you hear a click when the A/C comes on? If you don't then maybe your clutch(it's magnetic) is always engaged?

BCP43002

A low idle problem could be caused by(among other things) a bad A/C signal circuit or a bad fuel pump control circuit.

sakataj

iTrader: (182)

actually....OP the only major component that will draw power on the hvac system would be the compressor (a few other things will draw power but shouldn't be enough to have substantial voltage spikes)

that ACTUALLY wont tell u the compressor is on...the light will come on either way. all its doing is getting power to the switch...although i THINK (im not sure so dont quote me) it will blink if if the compressor isnt coming on but it will still light up

e-man

I agree. The light stays on regardless of whether the compressor is engaged.

Hey, sakataj, if you have a minute, could you take a look at the other thread on this topic near the top of the 2GS forum. You should just look at the last few posts. I started that thread a few years ago, and I've been posting to that thread as well (along with engin_ear).

sakataj

iTrader: (182)

i will be happy to...i dont know if u are familiar with me but i manage a HVAC suppply house so im familiar with most of this (automobiles arent my HVAC specialty, although they share the same priniciple theories/features)

yeah i clicked on it....no way i have time to read 121 posts. i will read last few as u said and we'll talk and see if we can get you working in the right direction (no im not saying im gonna fix this for you, im just offering to help with what i DO know)

e-man

I didn't know that about you. I do remember you from a few years ago, though, when I used to post on CL much more frequently than I do now.

Right, if you have a sec, just take a look at the last few posts and you'll see what I'm talking about.

I'll try to summarize the issue here. It's pretty simple. I've always had the low idle problem, however, with the a/c on and the outside temp above 32 degrees, the idle was fine. When the temp outside dipped below 32 degrees, I had low idle. I assumed it was because the compressor was always on above 32 degrees and off below 32 degrees.

Last summer, my compressor went out on me, so I replaced it. The a/c was fine for the rest of the summer.

About a month ago, when the temps got warmer here, I discovered that I had no a/c. Lexus took a look at it, said the freon was low, and recharged it. They also added dye to see if there was a leak. It's been about a month since the freon recharge, and while the a/c is blowing cold, there is something that is turning on and off now that didn't use to turn on and off before that is giving me low idle, even if the outside temperature is above 32 degrees, when I never had low idle before.

So the question is, why after the freon recharge is the system behaving differently than it did before the recharge? I think you said that the only part of the climate control system that draws enough power to affect the idle is the compressor. So, is it safe to say that the compressor is turning on and off now more frequently than it did before the recharge? Is it possible that the compressor was always on before the recharge which is why I never had low idle? Maybe that's what caused the compressor to burn out in the first place?

sakataj

iTrader: (182)

check your other post...this way we not talking in 2 posts.

the reason it could be behaving like this is the exact issue i address in the other post. if they over/under charged it u can be hitting a high/low (or over/under pressure sensor if u wanna call it this) which will turn the compressor on/off. if u hitting one of these, then YES it is possible the compressor is kicking on/off more than it did before the recharge

as i said get the pressures and we'll go from there....