Added A/C and now idle is too low/rough

[chevy72blu]

I had an A/C shop install a factory style A/C unit in my factory air 72 C10 with a 98 F body LS1. I know nothing about how to install A/C, and I dont care to learn at this point in my life. I drove the truck without air for years, and it idled smooth and ran great.

With the additional load from the compressor, it now idles around 550 RPM in gear. Obviously, the motor is unhappy about this. Switching the AC on doesnt stall the truck, but it is close.

My swap harness is from PSI.

Is this as simple as bumping the idle and in gear RPM a few hundred in HP Tuners?

It seems the factory way is to use the PCM to do this, with a signal wire indicating that the A/C is now on. This seems more complicated, and it's not how it is currently setup.

My truck is a basic driver and if "it works, it works" as far as I'm concerned.

[Jason Banks]

I would definitely bump the idle first. That is going to be the absolute easiest way.

The harder way would be to install a pressure switch in one of your lines and wire it into the ecu factory style. There's a couple thread on here how to do it.

Here's the fittings and pressure switch:
https://bp-automotive.com/product-ca...-conditioning/

[Jason Banks]

I just took a peek at my tune and the lowest it ever goes is 700rpm. Never seems like it's idling too high, and idles fine with AC on.

I don't have any AC feedback into the ECU...

[clay68c10]

Factory style, you would let the PCM control the compressor. It takes a little wiring, but isn't too complicated. Basically, the 12v signal currently going to the compressor clutch goes to the PCM instead and then the PCM triggers a relay to turn on the compressor.

You can add the refrigerant pressure sensor if you also want the PCM to run electric fans, but it's not needed for the idle speed adjustment.

*edit* Or just bump it to 700 like Jason Banks is doing.

[Accelo]

I had a similar issue and could not keep a reliable idle. I am using the exact same LS1 as you have installed. I have a BTR Stage II truck cam with a LS6 intake and headers. It was unsettling as any time I stopped I was not sure if the motor was going to die or not. As the idle is controlled by the computer using the idle bypass I wondered why the system would not control the idle better. Even with out the computer input that told the ECM the air conditioning was engaged. After getting the motor tuned all my issues with idle dissipated. The tune was $550. At the time I thought is as an expensive but not really necessary addition. I was wrong, if you have changed the camshaft a tune is mandatory in my humble opinion. AFTER the tune I had 354hp at the rear wheels. I didn't get a BEFORE reading as the AF was so far off the tuner thought one could possible do engine damage.
If you have a non-factory cam and a factory stall converter it can also affect the chances of getting a solid idle with the air on.
There are several well written articles on this very issue "Air Conditioning inputs to the ECM. Seems it changes depending the the year and model of the transplant. I was able to get mine to work. Wish you the same.
Cheers

[chevy72blu]

I appreciate the replies.

The motor is also WAY down on power, so I'm thinking my problem is twofold. I think it is a combo of the additional load + some ignition or other issue. It is a stock LS1. No codes via the OBD2 port, but I dont have a copy of HP Tuners myself and I'm sure swap tunes are very lenient on throwing a CEL.

I tried to get in touch with the tuner who did it originally 10 years ago, but he is swamped for a year+ and recommended another shop.

I wish I had time to mess with this stuff like I did when I joined this place. Now I'm at the mercy of various shops.

I might run through plugs and coils this weekend just to see if it is something simple. This thing used to run extremely healthy and strong, and now it will not break the tires loose from a standstill. It sat for about 2 years before going to the AC shop, so who knows.

[clay68c10]

Is the fuel fresh or is it 2 years old? Did you run it during that timeframe?
Old gas won’t do much for it, and these injectors like to plug up when they aren’t run.

I wouldn’t throw money at coils, if they’re bad you’ll get a misfire code and/or coil electrical circuit code.

[87chevy.com]

Before tunning to the tuner, id recommend making a ac harnesses.