# AC kicks on, then off.



## papereater (Sep 16, 2016)

People,

2001 civic EX, 1.7L engine, original owner. Was blowing warm air from vents. So I got home, shut car off, then started it again to observe. I watched patiently the clutch for 4-5 minutes (while noticing vents were blowing warm), then clutch kicked on, and vents started blowing cold! 

Clutch ran for say, 3-4 minutes, then quit. It did not turn back on for the next 4-5 minutes, and of course, vents blew warm air again. Guages showed 40 psi low, 125 or so high psi. I know there has to be enough gas in the system as otherwise it would not have blown cold (right?). 

So, the compressor has to be geting the 12V it needs, but why does it not kick back on in a reasonable time period? 

Thanks, people.


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## carmusic (Oct 11, 2011)

typical low gas, does it on my civic 07 when low on gas


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## papereater (Sep 16, 2016)

carmusic said:


> typical low gas, does it on my civic 07 when low on gas


Thanks, Car, but I smell a fish- psi's were 40 or so low side, hardly low for psi, Im guessing. 25 would be low to me. But you may be onto something- I will take readings again and report back. Low gas is better than a new comp....


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## raylo32 (Nov 25, 2006)

One thing to consider... even in a properly charged system the compressor will kick on and off when cooling demand is low. Here's a handy R-134a reference chart. The pressures will vary ~ in those ranges as the compressor runs and cycles on an off.

https://www.jamcoautoparts.com/systempressuretroubleshootingchart/


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## papereater (Sep 16, 2016)

raylo32 said:


> One thing to consider... even in a properly charged system the compressor will kick on and off when cooling demand is low. Here's a handy R-134a reference chart. The pressures will vary ~ in those ranges as the compressor runs and cycles on an off.
> 
> https://www.jamcoautoparts.com/systempressuretroubleshootingchart/


Wow- thats a handy chart, Ray! So, I should be getting about 50 psi low side, and 250 or so high side with a temp outside of about 85-87 degrees, right?

Looks like I am a bit low psi on the high side with my engine/system running. Maybe sign of a comp on its last leg. Still, mystery- how could it behave well for a few minutes producing cold air? Then quit for a very long break?


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## raylo32 (Nov 25, 2006)

Yup...and with that high ambient temp you should not be having an issue of low cooling load. Make sure to have the inside fan running on high... and it is really better to also put a fan on the outside condenser to get some airflow over it. Watch the pressures as it cycles. If the system is low on refrigerant it will pull the low side down to below the LP switch setpoint and it will cut off prematurely. The switch should activate somewhere in the upper 20s to about 30 psi IIRC, but it shouldn't do that whilst it is 87 degrees out and properly charged.



papereater said:


> Wow- thats a handy chart, Ray! So, I should be getting about 50 psi low side, and 250 or so high side with a temp outside of about 85-87 degrees, right?
> 
> Looks like I am a bit low psi on the high side with my engine/system running. Maybe sign of a comp on its last leg. Still, mystery- how could it behave well for a few minutes producing cold air? Then quit for a very long break?


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## papereater (Sep 16, 2016)

Ray, will remember all this when I get home, and try this out. Will be taking notes, as too many #'s to remember.....


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## papereater (Sep 16, 2016)

Connected the guages started car, with ac on I heard rattling/noises from comp. Was getting cold ac at vents, but geez- the needle on the high psi side was twiching/vibrating violently! Never seen this before! I couldnt even read it. Still cold ac, ran for 5 or so minutes, and needle slowed down a bit, reading 220-350 psi. Yes. No steady reading. Rattling decreased a bit. Shut off the car. 

Gotta be a ready to explode comp, right?


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## raylo32 (Nov 25, 2006)

Doesn't sound good. It does sound like the compressor might be failing... or it could be the clutch on it or clutch bearing. I don't know how to tell you to diagnose that. If it were me I'd probably just replace it. But you want to do it before it really blows up and contaminates the entire system with debris. I have been there and done that and it makes the repair 4x harder.


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## huesmann (Aug 18, 2011)

Two points from recent experience:

1) Some cars have a thermal switch on the compressor to keep it from running too hot—it turns off the A/C if the compressor gets too hot. Sometimes these switches can get stuck in the "too hot" position.

2) Not sure if all, but on some cars the A/C clutch is made up of two "cups" that are bonded together with a rubber ring. The inner cup is attached to the shaft of the compressor, and the outer cup is attached to the actual friction material of the clutch. The rubber ring can delaminate so that the cups are able to rotate independently. Well, actually the outer cup will rotate with the belt when the clutch is engaged, but the motion doesn't get transmitted to the inner cup because the rubber has detached.


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## papereater (Sep 16, 2016)

Sheesh- dumb things can happen, I learned after stumbling around the area that the scary rattling was n ot coming from the compressor, but from a loose exhaust manifold aluminum shield!!! Sorry, people, if I scared anyone here.....LOL

Turned out after adding about a 1/2 can of R134a and ran the car a day/2, the whole thing fixed itself! Who would have figured! Why it was blowing cold, then hot, must have been on the threshold of low gas supply. Anyway, thanks to all here who supported my dilema for a few days!


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## raylo32 (Nov 25, 2006)

Now you need to find and fix the leak!



papereater said:


> Sheesh- dumb things can happen, I learned after stumbling around the area that the scary rattling was n ot coming from the compressor, but from a loose exhaust manifold aluminum shield!!! Sorry, people, if I scared anyone here.....LOL
> 
> Turned out after adding about a 1/2 can of R134a and ran the car a day/2, the whole thing fixed itself! Who would have figured! Why it was blowing cold, then hot, must have been on the threshold of low gas supply. Anyway, thanks to all here who supported my dilema for a few days!


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## papereater (Sep 16, 2016)

raylo32 said:


> Now you need to find and fix the leak!


Right- I know its coming. I have a hunch where it is, but right now its a very slow leak. Its the removable low pressure line, where aluminum tube converts to (crimps to) rubber- leaking oil from the system........


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## huesmann (Aug 18, 2011)

Got a UV light?


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## papereater (Sep 16, 2016)

huesmann said:


> Got a UV light?


Sorry for late reply Hues, but geez, yeah, I do have one! In the drawer, new, never used! But I dont have the special glasses. Think it would still work without glasses, maybe in the dark? As I said, I suspect where the leak is but would be nice to shine that light on the hose, and verify that, right?


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## surferdude2 (Nov 21, 2019)

Squirt or dab with a rag some soap solution on it and watch for bubbles. 50-50 dawn and water will do. Beats a $100 electronic detector in most cases.


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## raylo32 (Nov 25, 2006)

I have one of those combination UV/electronic sniffer tools... I believe is is a Mastercool brand. You need dye in you system, of course, to use the UV, but the sniffer can get you in the ballpark of where to check with dye or soap bubbles.


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## huesmann (Aug 18, 2011)

Problem with soap is where you have the radiator fan blowing any bubbles away.


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## raylo32 (Nov 25, 2006)

Same issue for the sniffers with the fans dispersing the leaked refrigerant vapor. But sniffers still might help depending on where the leak is (good for inside sniff for leaking evaporator) and if you can work around the air currents in the engine bay. For vehicles with electric fans those can be temporarily unplugged.



huesmann said:


> Problem with soap is where you have the radiator fan blowing any bubbles away.


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## papereater (Sep 16, 2016)

But there is already pressure in the system for soap- even higher psi's if in the low side hose, so why would it be better to do a soap test with engine on(?). Anyway, good idea. Will try it maybe today......


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## Fixin_cars (Mar 10, 2021)

papereater said:


> Thanks, Car, but I smell a fish- psi's were 40 or so low side, hardly low for psi, Im guessing. 25 would be low to me. But you may be onto something- I will take readings again and report back. Low gas is better than a new comp....


Try adding freon watch gauges for fill and measure vent temp with thermometer


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## Fixin_cars (Mar 10, 2021)

raylo32 said:


> Yup...and with that high ambient temp you should not be having an issue of low cooling load. Make sure to have the inside fan running on high... and it is really better to also put a fan on the outside condenser to get some airflow over it. Watch the pressures as it cycles. If the system is low on refrigerant it will pull the low side down to below the LP switch setpoint and it will cut off prematurely. The switch should activate somewhere in the upper 20s to about 30 psi IIRC, but it shouldn't do that whilst it is 87 degrees out and properly charged.


High readings usually double current outside temp and low aide 30 or less


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