AC start/stop every few seconds

[Blk00ss]

I noticed my son's '05 has been blowing recycled non cooled air recently. This truck has always been one to freeze you out, but not lately

Today I decided to start the vehicle and turn the AC on to see if the belt spun. It wasn't spinning at first, then it would spin for a few seconds and then stop spinning.

I don't much about the cooling system on this truck. I suspect it has some sort of pressure switch in the system which could be causing this start/ stop behavior. Is this a safe assumption? I'm not gonna rip the system apart myself, but is there anything else I should be looking for that could cause this on/off issue?

 

[OR VietVet]

Safe assumption is a leak in system.

 

[Blk00ss]

Safe assumption is a leak in system.

I'm sure there is. But what I'm wondering is if the system has some sort of pressure check that allows the system to run if a certain pressure is detected/ not detected. I read somewhere that the system could be kicking on/ off because the pressure is fluctuating. So it reaches a pressure that allows the compressor to kick on, but then it kicks off when that pressure drops. Wasn't sure if these systems had that same capability.

 

[corvette744]

I'm sure there is. But what I'm wondering is if the system has some sort of pressure check that allows the system to run if a certain pressure is detected/ not detected. I read somewhere that the system could be kicking on/ off because the pressure is fluctuating. So it reaches a pressure that allows the compressor to kick on, but then it kicks off when that pressure drops. Wasn't sure if these systems had that same capability.

Have someone put gauges on it sounds low on freon to me.

 

[OR VietVet]

Yes, on the gauges and it is low enough that the low pressure switch is sometimes allowing the compressor to come on and then kick off. That is what it sounds like based on your description. By the way, the belt always spins. It is whether or not the clutch engages and spins with the pulley.

 

[Blk00ss]

Yes, on the gauges and it is low enough that the low pressure switch is sometimes allowing the compressor to come on and then kick off. That is what it sounds like based on your description. By the way, the belt always spins. It is whether or not the clutch engages and spins with the pulley.

This is the kind of answer I was wanting. Not " it sounds like its low on Freon to me" responses.

I KNOW its probably low on refrigerant. Its an '05 that has never, not one time needed AC work. My question was does the system have something in place to detect low pressure which would cause it to kick off

Thank you for this answer! So to clarify, the belt should spin at all times? Not just when the clutch on the compressor says to? Any idea if a bad tensioner could keep a belt from spinning freely? I ask because when I watch it, i see it spin, stop, spin again all within a few seconds.

 

[OR VietVet]

There is a tensioner. If you lift the hood and look straight down at the front of the compressor, look just to the right of the front of the compressor and there is the belt going over the tensioner. It is spring loaded and would have to be broken in order for the belt to just hang there and not spin with the engine speed and turn the compressor pulley. The belt is around that pulley on the compressor and turns the whole time the engine is running. When there is enough pressure in the a/c system, the low pressure switch, that is mounted at the accumulator at the passenger side firewall area, activates the clutch in front of the compressor pulley and locks it against the pulley that is turning with engine speed. That clutch is splined to the shaft of the compressor and then turns the a/c compressor innards and works the a/c system, for lack of a better term. That belt turns all the time the engine is running but the clutch at the front of that a/c belt pulley does not turn until the low pressure switch allows it to engage that pulley. If the pressure gets too high in the system, there is a high pressure switch, again for lack of a better term, that will shut the system down if pressure is too high and that protects the a/c system.

But again, from what you describe, it sounds like the low pressure switch is intermittently allowing the clutch to engage with the belt pulley at front of compressor and that typically means that the pressure is low but not completely empty.

 

[BoatyMcBoatface]

Your system is low on Freon. If you jumper out the switch using a paper clip it will force the compressor on. this happens every 2 or so years on my yukon and i just add a bit of freon and it works fine all summer. You may have a leak at the shrader valve on the low side. Thats the usual culprit where a slow leak starts. When you add freon get the one with the UV dye in it and that way next time its low you can see where its leaking from. But again 22 year old system and i always see the shrader leaking.

 

[Blk00ss]

Your system is low on Freon. If you jumper out the switch using a paper clip it will force the compressor on. this happens every 2 or so years on my yukon and i just add a bit of freon and it works fine all summer. You may have a leak at the shrader valve on the low side. Thats the usual culprit where a slow leak starts. When you add freon get the one with the UV dye in it and that way next time its low you can see where its leaking from. But again 22 year old system and i always see the shrader leaking.

Thank you! This is what I was looking for. There is no doubt our '05 has sprung a leak. But I really wanted to know where the "typical" leaks were from within the system.

 

[OR VietVet]

You can also look for leaks at the connection/o-ring locations and at the crimp fit of the hoses. When it does leak, a/c oil will come out with the refrigerant and those areas will be wet and attract dirt that will gather and cling there and show as wet looking dirt.