I'm having a strange issue where my A/C only works above 1500 rpm. Wont run at idle or below 1500. Replaced the compressor and recharged. Same issue. Could this be a pressure sensor issue or something to do with the throttle? Runs fine while driving and even holding rpm to 1500 at stops. Very annoying obviously. Fans work etc. RPM does raise at idle when A/C is turned on, so it does know it should be turning on, but it doesn't actually engage the compressor.

Thoughts?

 

Like the clutch doesn’t engage until the RPM’s hit 1500? And you evacuated the whole system before you recharged it?

 

Have you performed pressure tests on the Low / High side of the operating A/C system, taking into account the ambient temperature?
This will tell you the most about it.

 

Yes I have an A/C machine at my shop. Pressures are fine when the compressor is running. New compressor, fresh charge, and today I replaced the trinary switch hoping for a fix. Same issue after replacing/recharging. I'm pretty sure this has something to do with my engine build/computer tuning at this point. There is something to do with rpm, throttle, or load detection that isn't being seen as plausible by the computer. Will have to do some circuit research and see what I come up with.

 

I don't think it's an engine control issue. The A/C on my GS300 runs from idle. The ECU raises the idle from 750 rpm to 850 rpm when the A/C clutch is engaged.

Usually, higher RPMs required to operate the A/C are a sign of insufficient compressor performance. Does this aftermarket compressor have less performance than the OEM?

 

It's a new Denso unit. Didn't cheap out. I found that at idle, there is no power going to the compressor clutch. Power is supplied to it at 1500 rpm and above. So there is a control not allowing the clutch to be powered below 1500 rpm. If it had power supplied but wasn't running, I'd be looking at the compresor again.

 

What is the ambient temperature around your vehicle? Can you connect the TechStream scan tool to OBD-2 and see what the ambient temperature sensor is reporting to the ECU? I assume you have a wiring diagram for the car's air conditioning. I highlighted the important points on it.

 

Ambient sensor is reading fine, in fact I replaced it with a Toyota OEM one less than a year ago. I'm thinking it's missing an input to the ECU below 1500 rpm. The tach, rpm, and throttle data have all been modified for my build/manual trans swap.

 

I think I've found where I need to mess around. I was going through my schematics and it hit me. The ATEMU (Auto trans emulator) I had to wire in to run the manual swap has several hints in the instructions that it affects rpm inputs to the ECU. There are different settings and even different ways to wire certain pins under certain circumstances. Currently I am set up how it shows, but in the section below, it gives different options. I may have to screw around trying different combinations of pins and settings.

 

Now that makes more sense, with all your manual transmission swaps and modifications you may have incorrect RPM data being sent to the ECU which affects the A/C clutch sequencing. All my suggestions were based on a stock vehicle configuration.

 

I appreciate the input from you guys, I'm sure it has to do with my mods. If I can't figure it out I'll give it to my tuner. Had a brain fart for a minute, but it's very likely a tuning issue at this point.