an1176

Hi folks I have some AC questions. First I have a 94 22re 4x4. My AC has never worked right. It blows cool not cold. While working on it last year I realized my AC idle up VSV was not working along with compressor and who knows what else. Long story short, with summer months coming up I ordered all new AC stuff. From compressor, expansion valve, condenser all of it. I ordered a used VSV from ebay since mine was shot. While waiting on my AC stuff to come in I hooked up the VSV to see if it would idle my truck up. It did for a moment then stopped. I let truck run for some time and truck never idled back up to kick on the compressor. If I manually give it gas the compressor kicks back on. I drove down the road running errands with the AC on and every time I come to a stop my idle fluctuates between 450 and 900 several times. While doing this with the idle fluctuating I can hear a click pause click from behind the dash, sounds like your blinker relay. I've messed with the AC idle screw (black one) to see if that will adjust the idle to where the compressor would stay on and it has no effect. Anyone have any ideas?
Thanks

grumpin

Your A/C Amplifier, under the dash, by the evaporator, controls the Idle Up VSV. I'm assuming you're hearing that. If your pressure isn't correct, either too high or too low, the Amplifier could be cutting it in and out. I would get everything new on and the proper pressure, then you'll know if the VSV and Amplifier are working correctly. Also on mine, occasionally when I come to a stop my A/C will cycle like that. I turn the A/C switch off then back on and it stops. I don't know why it does that, and won't be able to troubleshoot until it always does it.

an1176

Thanks grumpin. I had no idea there was an amplifier until today. I did some research earlier and found out about it. I plan on putting all new stuff in this weekend. Hopefully this will fix it. Thanks again

scope103

Grumpin is correct. The A/C idle-up valve does NOT control the compressor. You're probably low on refrigerant, so at idle speed the compressor can't hold up the pressure and it's shut off.

I assume you're going to upgrade to R-134a (staying with R-12 requires a fancy license and is very expensive), so you'll need to replace the o-rings. Which you probably want to do anyway since something is leaking somewhere.

Here's everything I know about A/C: https://www.yotatech.com/forums/f116...-r134a-284801/

an1176

It's been already upgraded. The odd thing is the idle up vsv isn't kicking in the compressor but if I manually raise the idle (giving it gas) the compressor comes on. Is that right?

grumpin

No, that's not right.

an1176

So there is something wrong with vsv or amplifier if I can raise idle and get the compressor to come on?

scope103

Do the easy stuff first. If you have insufficient refrigerant (less than 30 psi) http://web.archive.org/web/201102052.../4generald.pdf the compressor isn't supposed to start. While this doesn't perfectly match your symptoms, check the refrigerant level first. http://web.archive.org/web/201102052.../8inspecti.pdf A good gauge set will set you back $60.

an1176

I'm replacing everything tomorrow. I'm 99% sure it's charged right. There something wrong with the compressor, expansion valve, or something else. Sorry I don't know much about ac stuff. That's what I was told by a buddy that's a good mechanic. So with it charged right and something else being the issue, should the vsv and amplefier work right? Truck should idle up and run the compressor even though the system is messed up somewhere. Thanks for the help folks.

grumpin

I agree with scope, you need to make sure it's serviced correctly. I don't want to doubt your buddy, but how did he know it was serviced correctly if the compressor isn't engaging properly. The VSV isn't going to affect the compressor, the Amplifier signals the VSV. Yes, your Amplifier could be at fault, but I wouldn't change it until I knew for sure it was bad. With fairly inexpensive gauges you can check your system.

ozzir70

Doesn't the amplifier control the rpm that the compressor kicks on at? I thought it was between 600-1200. there is an adjustment screw on the front of it. I just got my new ac lines from Toyota today. I'll be doing the install sometime soon. I have already added the new evaporator in the cab with a new expansion valve. I am just waiting to get the new compressor and condenser. so i'll be watching this post closely

grumpin

The Amplifier signals the VSV, the RPM adjustment is on the Intake Manifold. It's the slotted white knob under my hand. You can see the VSV connector to the right.

ozzir70

So then what is the adjustment knob on the amplifier for?

grumpin

Good question. The FSM doesn't have anything about that. Some quick research states that it adjusts the RPM that the Amplifier will engage the compressor. So it won't engage it at too low of RPM. Which could explain the OP's symptom. Very interesting! More learned about this system today!

scope103

No.

That is the idle-up speed adjustment -- it adjusts how much the idle is raised when the compressor starts and the ECM commands the VSV to open. There is no feedback to the ECM; it has no idea where that screw is set. http://web.archive.org/web/201102052...23vacuumho.pdf

The adjustment on on the amplifier:


is to adjust the speed at which the compressor stops at idle. Unfortunately (for this post) I didn't have to adjust mine, and I can't locate here in Yotatech where someone described which way is which. But I'm 80% certain that you want to adjust that control so that the compressor continues to run once the idle-up raises the idle.

grumpin

Again, interesting. So, I assume that's idle or better yet VSV idle RPM, how does the Amplifier distinguish between idle RPM and throttle up RPM?

scope103

You need to try that question again.

The VSV is opened when you press the A/C button. What happens as a result depends on vacuum plumbing (and the adjustment of that white screw).

The A/C Amplifier has an ignition pulse input, from which it could get the rpm. Whether set by idle up or your lead foot. It can then use that (controlled by the adjustment ON the amplifier) to decide whether to engage the clutch.

http://web.archive.org/web/201102052.../2aircondi.pdf

grumpin

OK, I see what you meant. But, doesn't that mean too low of RPM for the adjustment? I see that the Amp gets a signal from the ignition and ECU but no signal back. How can it adjust the idle up if it's done by vacuum via the VSV? My thinking is that it won't engage without enough RPM. Or we're saying the same thing different ways and it hurts my brain!

scope103

The same way the power-steering idle up works. It just short-circuits add'l metered air into the plenum, which is the same as nudging the throttle open a little. You can't adjust the PS idle-up, but you can for the A/C. I don't know why the difference.

grumpin

Right, I know that, but you're not adjusting the idle up at the Amp, which is my point. The adjustment at the Amp has to be for a minimum RPM to engage the compressor. Not idle up speed adjustment, because it's done at the Plenum.