Hey guys, I could use your help on an issue with the A/C compressor. When the car is at idle the compressor clicks on and off very rapidly. If I keep the system off until I'm driving and them turn it on it works just fine.
I'm having a friend of mine look into it and last night we noticed that if we held the high pressure switch wiring it would stay on. Thinking that the wiring was the issue we de-pinned the connector and refreshed the wiring. He is an AP mech and I am in mil-aero wire sales so we both know wiring and how to do it properly.
We reconnected the connector, started the car and we are still getting the clicking. So we checked the switch and it ohms out o.k. We also checked the pressure in the system. It was late last night but if I remember right the high side was in the 150s and the low side was 120s static.
I think that's all we did until it was time for me to crash. We are going to be taking another look at it today and I'm hoping someone here can shorten our learning curve. The one thing we couldn't find was the low pressure cycling switch. Is there even one on the car and if so where is it? Oh and we also tried another high pressure switch from another Vette and that didn't fix it either.
By the way my car is a 04Z.

Thanks for the help

 

What does "refresh" the wiring mean? When you manipulated the wiring, the compressor stayed engaged. Did you check the resistance on the wiring, while moving it around, to see if it broke continuity?

 

I had the same thing happen on my 02 last year. Rapid clicking from compressor, actually was the clutch on the comp engaging and disengaging rapidly. Turned out I needed a freon recharge and it's been working fine since. Hope this helps, good luck!

 

I agree!!

 

What I mean by refreshing the wiring is that we de-pinned the connector and soldered in new wire because we thought the wiring might have broken. Don't think that's the case. We tested the switch and that seems to be passing inspection, but we are still getting a/c issues when the car is idling. If I'm driving down the road over 2k rpms then it seems to work fine. Car runs a little harder but the a/c is blowing just fine.
I'm curious what pressures you guys were seeing when you needed to charge the a/c. I've posted the results from mine in my first post. Thanks.

 

Just an FYI, my original compressor on my '99, developed a rattle sound yet worked very well. This went on for a while and I was able to determine it was not the compressor clutch. Eventually I replaced the compressor via the dealer and the rattle was gone. Now this wasn't a clicking sound but who knows. Did this sound just start? Can you see if the clutch is disengaging from the compressor when the clicking is happening?

 

Your R-134 Charge is LOW! The compressor suction pressure (low side ) is dropping below the compressor cut off pressure.

Get a can of R-134 (WITH OIL) from Wallymart. They come with a hose and gage. Shake the can well and connect it to the LOW side connection (close to the fire wall area).

Turn the AC on and press the button. KEEP THE CAN UP-RIGHT to allow gas to enter the system. Have someone raise the engine RPM to 1000-1200 while you charge. Charge till your around 25-30 on the gage. STOP CHARGING to get an accurate system pressure. If you shake the can up and down while charging, you can raise the pressure inside the can a little to speed the charge. DO NOT turn the can up side down as that will inject LIQUID R-134 in the gas side of the system!

If you want to speed up the process, you can sit the can in a can of hot water while your charging.

Make sure that both doors are open, the fan is on full speed and the system in selected to fresh air and center vents. As you charge the center vent should get cold!

BC

 

Thank you guys! I'll hopefully be able to knock this out sometime this week. Tonight is my middle child's 4th B-Day so I'll be busy with a Pirate party
Bill, Thank you for the step by step. I'll swing by Wal-Mart and give it a go. One final question: When using the can from WallyWorld what final pressure am I looking to achieve?

Thanks.

 

The final pressure depends on the outside air temperature. Higher ambient temperature will result in higher refrigerant pressure in the system.

With the outside air temperature in the 75-85 degree range, the evaporator pressure should be in the 25-45 PSI range, when the correct refrigerant charge is reached.

 

O.k. guys, I'm back for more help. I purchased a can of R134 w/oil per Bill's instructions. I don't have much help when I work on my car since I normally do it after my three little ones are in bed. So, that pretty much knocked out revving the engine in the basement. I used an Advanced Auto parking lot this time.
In order to keep the rpms up I used HP Tuners' Scanning software and just adjusted the rpm level that way. It worked quite nicely by keeping the rpm level constant.

Here are the steps that I took:
1) Drove to Adv. Auto
2) connected HP Tuners
3) Hooked gauge w/ can to low pressure port(near the firewall)
4) Went and adjusted the rpm to 1150
5) turned A/C on full blast, 60 degrees with fans at full speed

--My observations:
ambient temp in southern TN about 80-85
-when I first hooked up the gauge the pressure reading was 150, in the red
-after I up'd the rpm and turned the a/c on the pressures gradually fell to around 65
-a/c ran absolutely fine, blowing cold air as long as the rpm was up
-commanded rpm level to 800, which is where it is normally set, and the a/c clutch started kicking on and off again and the pressures were jumping all over the place.

I decided since the pressures were so high that it probably wasn't wise to add more into the system. Now I'm wondering what it could be. Is there too much pressure and do I need to relieve some to get the pressure down? Is the compressor bad causing all the fuss? Why is it when the rpm level was commanded at 1150 or so that everything worked just fine? Could it be the UD pulley that I had installed when I swapped the cam and could that be causing a dying compressor to not get the "juice" it needs to run without getting up to the 1100ish rpm level.
Again, thanks for the help.

 

Your UD damper pulley probably isn't allowing the compressor to run efficiently, or at full capacity, at low RPM's.

What percentage of underdrive is the pulley rated at?

 

It's a 25% underdrive pulley. Even if the UD pulley isn't allowing the comp to operate at full capacity at idle is there anything I can do to help that? Or would I have to run the idle rpm up to 1000 to compensate?
Surely others here are running similar mods to me and still have their a/c.

 

Seems like you're just shooting in the dark here. There is a comprehensive test in the service manual, which examines low/high pressure, both static, at RPM, etc. Are you using a service manual?

 

Increasing your idle speed will help, but I personally don't care for having to do that kind of trade-off.

 

I have the SAME UNDERDRIVE PULLEY and ZERO AC ISSUES! So,, I seriously doubt, its an under drive pulley issue. IF,,,,, your reading the LOW (suction Side) with the engine idling,, you still should see 25-30 PSI!

I can NOT see why you would read 60 PSI "UNLESS" one of the following things are wrong:

1. System is overcharged.
2. Orifice Restrictor and screen is clogged.
3. BOTH

There is a possibility that the pressure sensor could be bad! It’s a solid state device so, it’s a possibility that it not functionally properly causing the compressor to cut in and out at the incorrect system pressures.

WHAT does the HIGH SIDE read??? Another QUESTION.. If it TOO HIGH, same thing. It will cause the compressor to cut off and on to regulate the pressures.

YOU CAN change out that pressure switch without depressurizing the system. It screws on to a Schrader valve and the valve shuts when you remove the sensor. NOTE. Remove the pressure sensor SLOWLEY just in case, the valve fails to shut!!!!!!!!!!!!!

Read the HIGH & LOW sides and compare them to the service manual for the correct outside temps and humidity and proper system set up parameters.

BC

 

No I'm not using a service manual. And yes, I am somewhat shooting in the dark, but I'm doing my best with the knowledge that I have. I was throwing out ideas after the work I tried to do post Bill's advice didn't seem to match up to what I was expecting.
If we all had service manuals and had the off-hand knowledge to fix our cars then this forum would be somewhat useless. It'd just be pics, timeslips and dyno sheets. Although it certainly would be pleasing to see a bunch of pics, the rarity of this forum is that the knowledgeable folks dive in a try to help folks figure out what is going on with their cars.
If I have misread your post, I apologize. I've been driving around in 106 degree weather w/out a/c and I am a bit tired of doing that. Also, I'm trying to stay out of the dealership and to do so, I'm trying out ideas that folks have said has worked for them.

 

I see. Very well then. I'm sure Bill has plenty of great suggestions for you.

Good luck.

 

I disagree about the orifice tube and screen being clogged.

If that were the case, the suction side would be reading very LOW, and the discharge side would be reading very HIGH.

 

Sounds like its time to take it to a professional AC shop and have them check it properly. The dealer might still be a good idea because they have a Tech 2 and they have the manuals.

 

Any competent A/C shop can make a proper diagnosis using a set of R-134a gauges connected to the suction and discharge ports. A Tech 2 is not essential to have for A/C service.