A/C clutch short cycles at startup

[TSandner]

2008, 2500, 4X4, Quad cab.
When I first start the truck the A/C compressor clutch will engage and then disengage in a short time, and will continue to cycle in this manner until I start to drive it down the road It only does this on initial startup. Once I start driving it will engage until the evaporator reaches the appropriate pressure and then it will cycle on and off as designed and cools the truck just fine. Even when I come to a stop, such as at a traffic light, it will continue to cycle and cool as designed. It only does the short cycle at initial start up. I have tried pressing the accelerator and holding a higher engine speed while parked but it does not seam to make any difference. The only thing that will get it to work correctly is starting to drive the truck. I don't need to be going very fast so I really don't think it's airflow through the condenser.

 

[jghflys]

My truck has done that since I got it. I changed the compressor, liquid tube, accumulator/dryer and condenser when I installed a rebuilt engine about 215 K miles due to broken rings in the original engine. Still does the same thing. I chalked it up to the system getting to equilibrium. It cools fine. I have had gages hooked up on startup and saw pressure going high when it cycled. Then it ran normally withing a few cycles.

 

[RVTRKN]

You might be confusing the noise, when liquid that collects in the compressor, if it sits over 24 hours will have a loud start. Its a flaw that they located the compressor below the Evaporator. If its hot, its even more likely to do that, because refrigerant moves to the cooler section and with the compressor on the bottom makes it easier. My 04.5 did that with and my 07 C&C did that, and after replacing the compressor I installed the new one with a 10 watt heater on the bottom, which eliminates the harsh startup.

 

[TSandner]

You might be confusing the noise, when liquid that collects in the compressor, if it sits over 24 hours will have a loud start. Its a flaw that they located the compressor below the Evaporator. If its hot, its even more likely to do that, because refrigerant moves to the cooler section and with the compressor on the bottom makes it easier. My 04.5 did that with and my 07 C&C did that, and after replacing the compressor I installed the new one with a 10 watt heater on the bottom, which eliminates the harsh startup.

I can open the hood and watch the clutch engage and then disengage within about 1-2 seconds.

 

[RVTRKN]

I have never seen that, but I wasn't looking when it would bang. Seems like yours is different, did it bang while doing this?

 

[TSandner]

I have never seen that, but I wasn't looking when it would bang. Seems like yours is different, did it bang while doing this?

No, it does not make any unusual noise like a bang.

 

[jghflys]

I can open the hood and watch the clutch engage and then disengage within about 1-2 seconds.

My truck cycles at about 5 second intervals gradually increasing as the system reaches equilibrium. No unusual noises at all. As I stated earlier, I replaced the compressor, liquid tube, accumulator/dryer and condenser when I installed a rebuilt engine. The system was still cooling fine after 215K miles and I replaced the components because of miles and years of age and ease of access with the engine removed.

 

[Tuesdak]

How old are the fan clutches in your trucks? The AC system will suffer and fail from overheating long before the engine notices a lazy fan clutch. Fan clutches take longer to lock up as they get older. Best test I have heard of is: The fan should be roaring in about a block of driving with the AC on from a cold start.

I assume the AC systems are not overcharged. That is they were charged by weight rather than: any other way like dumping a can in till it got cold.

Check the condenser for being airflow restricted aka plugged up with bugs, etc.

Are you idling with the blower fan on high? This is moving the most heat at idle to the condenser. No airflow over the condenser means it overheats. Overheating means high head pressure in the AC system that shuts the compressor off. Getting moving does two things: more airflow over the condenser and allows the fan clutch via higher than idle engine RPM to lock in and move more air. Run the blower on a lower speed setting till you get moving.

Better yet. Your years should have high idle: use it! Esp. for AC and warm up. More engine RPM means the fan clutch can kick in faster and move more air to cool the AC condenser.

Some others have put a small electric fan on the condenser to help keep the condenser cool. The 2003 I had wouldn't kick the AC clutch out and just popped the AC relief valve open.