General Maintenance & Repairs - --Resolved-- a/c compressor cycling rapidly, can't figure this one out

I found a little info by using the search, but not what I was looking for. Recently did heads and cam and got the car tuned. It idles fine with no a/c, but the compressor cycles rapidly at idle when turned on. If I increase the rpm the compressor will stay on. It only acts up at idle.

I hooked up the HP Tuners scanner and commanded the a/c clutch to engage while idling and it works perfectly when commanded on. As soon as I let return it to the car it starts cycling again.

I hooked up a can of 134+ (with built-in gauge) on it and it won't give me a correct reading at idle because the compressor is cycling so fast. I tried adding 134 anyhow and it didn't help the issue.

The cars idles great when the compressor stays on, but due to the constant cycling the idle surges up and down. Any ideas?

Are you sure it's actually cycling? Could just be the clutch starting to seize up.

Not seizing. I can command it on using HPT and it works flawlessly. No dragging either, just clicking on and off about every second, and only at idle.

Its either the relay kicking in and out or the low pressure switch causing it.

Probably the low pressure switch. You're brute forcing the clutch with HPTuners, bypassing the switch input. What you really need to do before you do anything else is hook a manifold set to it and verify your pressures are correct while the car is off. If the high and low pressures read right then I'd suggest you force the compressor on again and verify the operating pressures are correct. If all the pressures check out both times I'd start by replacing the low pressure safety switch.

Best of luck.

https://lh4.googleusercontent.com/-T9oeTEMBFEU/TlfubSuvwZI/AAAAAAAAI84/GYqItOYzyRs/AC_manifold_gauges.jpg

Easiest way to check the low pressure switch is to unhook the LP switch, use a paper clip and jumper the wires. Only do this if the LP switch has two terminals. If it has more disregard my last.

If it is the switch it will stay on continuously. As mentioned using a set of gauges is the best way.

Thanks guys. Wouldn't the ECU throw a code if the pressure switch is acting up though?

Thanks guys. Wouldn't the ECU throw a code if the pressure switch is acting up though?

I don't believe so, no.

Sounds most likely to be a low charge, which will not produce sufficient suction pressure to activate the lp switch, or the switch itself. Since it stays on when you give it throttle, I am leaning toward low charge. Just like everyone else already said, some gauges will do a lot of justice here.

I am going to replace the switch and see what happens. I was not able to jump the switch because it has 3 wires. But I did unplug it and the a/c stopped switching. If that doesn't fix it then I will take it to a buddy that is an a/c guy.

I think you have a slow leak and it's now too low.

It is low on freon, it is trying to turn on but when it does it finds it doesnt have enough pressure in the system so it turns off automatically. Go and have the system evaced and recharged, those junk cans you buy from the auto store that only hook to the low side are just that junk!!! They are not accurate and you need to know the high side pressures as well.

Thanks guys, I am going to have it checked by my buddy (a/c mechanic)

Id be interested to hear what you find out. I read this thread yesterday and after having my car torn apart for a couple days, i took it out for a drive and it did the exact same thing. Never happened before and now its not doing it anymore. Hopefully a low charge - I do enjoy my AC...

needs freon

For those that are interested, the a/c checked out just fine. It appears to be tuning related. Seems the IAC is not handling air flow correctly when the a/c is switched on. The a/c shuts itself off when the idle parameters are unstable. I should be able to fix it with a little HP Tuners time.

wow go figure. I remember when I was in school instructors saying "if you don't know computers you won't be able to repair a car" and we all laughed.

Well it is a side effect of the cam install, so it was not a problem stock. Just something a tuner should already be familiar with. I have been out of tuning for so long I had no idea :(

Ok thanks to JimmyBlue I got it resolved. I simply went into HP Tuners and zeroed out the tables for Stall Saver. Apparently this function will disable the a/c clutch when it thinks the car might stall out. Since the idle was a little unstable with the a/c on, it was turning off the a/c clutch and then allowing it to come back on when the idle would recover.

There is an "AC On" fuel table in hptuners. Don't disable stall saver. Just modify that table correctly to match the new cam.

I plan on giving it more attention when I have the time, for now I just wanted the a/c to stop cycling