AC compressor cuts on and off repeatedly - JeepForum.com
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post #1 of 16 Old 05-30-2015, 11:45 AM Thread Starter
djs99
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AC compressor cuts on and off repeatedly

1999 4.7L V8 Grand Cherokee - Turning on the AC blows very strong steady air but it comes out at ambient temperature. (And its HOT here in New Orleans!) I thought maybe a freon leak, so I bought one of those freon bottles w/ gauge attached. It was low, so I added about half a bottle until it showed full. But AC still did not blow any cold air, not even for a second.

Here is the strange thing - with engine on, AC on full blast (manually), attached the freon hose/guage, squeeze trigger to release freon - I hear the clutch kick in and gauge rises. But a second later, the compressor revs down and the needle falls. The I hear the clutch again, needle rises to full, then again it falls.

What would be causing this behavior? A bad clutch? Electrical problem? Freon leak? I would think that I would at least get some cold air. I'm probably going to bring this in to my mechanic on Monday but hoping to get a few suggestions before then.

Thanks!

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post #2 of 16 Old 05-30-2015, 02:07 PM
Vaporhead
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Those cheap gauges are not accurate. You need a proper set of manifold gauges that will show the the high pressure and low pressure. It is normal for a compressor to cycle, but if you were low on freon, you have a leak somewhere.
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post #3 of 16 Old 05-30-2015, 02:27 PM
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All things being equal, the more 134a you put in the system the longer the clutch on the compressor should stay energized. Around 25psi the clutch will cycle off. And proper filling like you are doing requires rpm's at or above 1500.
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post #4 of 16 Old 05-30-2015, 04:04 PM
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But if you add too much freon, the high pressure sensor will make the compressor shut down everytime it tries to come on. My suggestion would be to have someone with proper gauges check it. Or have an AC tech evacuate the system and put a proper charge (with oil). And he should be able to check for leaks as well. Just my $.02.
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post #5 of 16 Old 06-01-2015, 09:40 AM
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Probably a freon leak somewhere. AC Compressor doesnt work unless freon gets to it. My guess is its a minor leak bc it still comes on sometimes.

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post #6 of 16 Old 06-01-2015, 12:33 PM
alfaitalia
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Tell me you don't really use Freon that side of the pond......hopefully you mean r134a.

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post #7 of 16 Old 06-01-2015, 12:38 PM
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Quote:
Originally Posted by alfaitalia View Post
Tell me you don't really use Freon that side of the pond......hopefully you mean r134a.

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It's been adapted as a generic term for automotive refrigerant. But yes, R12 is pretty much impossible for the DIY'er to get a hold of anymore. R134A is the readily available refrigerant, at least until the new stuff, R1234yf, comes to market.

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This is easily the worst post, and thread, I have ever seen in 7 years of being on JF.
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post #8 of 16 Old 06-01-2015, 01:00 PM
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Quote:
Originally Posted by Jeeples
It's been adapted as a generic term for automotive refrigerant. But yes, R12 is pretty much impossible for the DIY'er to get a hold of anymore. R134A is the readily available refrigerant, at least until the new stuff, R1234yf, comes to market.
THANK YOU R134A = FREON SAME FRICKIN THING i just dont feel like typing R134A every time

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post #9 of 16 Old 06-01-2015, 02:35 PM
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Quote:
Originally Posted by Jeeples View Post

It's been adapted as a generic term for automotive refrigerant.
True, a weekend mechanic refers to R134a as Freon like one would refer to a receiver as a hitch, professionals know better. It's semantics that's not worth pointing out unless someone was being cocky.

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post #10 of 16 Old 06-02-2015, 11:48 AM Thread Starter
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I never realized that R134a was not the same as Freon. For the record, I did purchase and use a can of R134a.

When I have the car on, AC running full blast, it blows strong and steady, but ambient temperature. However, sometimes at idle I can see the RPM going up and down steadily, like a few hundred RPM difference, only when the AC is on. Going around to the front, open the hood, I can hear what I assume to be the clutch making a loud click sound, then rpm goes down, then back up, then another click, over and over again. (Maybe its the other way around - I don't recall if the click is after revving up or down.)

I drove it to my Mechanic's yesterday, but there were so many cars piled up in his driveway that I did not even stop. Will find someone else to look at this. But still curious to see if anyone here has any clue what's going on? Would a leak cause this behavior, a sensor, or a worn/faulty clutch? I just hope its not the compressor itself.
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post #11 of 16 Old 06-02-2015, 01:14 PM
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The clutch engages and compressor starts pulling a suction on the evap, if there is enough volume of 134a in the system it compresses the gas, it pulled from the evap, into a liquid and pushes into the condenser where it cools to ambient temp and heads back to the evap where there is a restriction that the compressor sucks against. AKA a orifious crimped in the low side line or a TX valve.

If there is not enough gas in the system the compressor will draw down the low side too far. There is a low pressure sensor in the system to prevent the compressor from drawing it down to low.

Look of the refrigerant cycle. Understand how it works and you will understand why the clutch cycles when some of the 134a leaks out.
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post #12 of 16 Old 06-02-2015, 04:15 PM
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Quote:
Originally Posted by Jeeples View Post

It's been adapted as a generic term for automotive refrigerant. But yes, R12 is pretty much impossible for the DIY'er to get a hold of anymore. R134A is the readily available refrigerant, at least until the new stuff, R1234yf, comes to market.
My Jeep has a sticker under the hood warning me not to use R12 in my a.c. system .....not that you can buy it here. Not seen that sticker on any others I've looked at. Strange.

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post #13 of 16 Old 06-02-2015, 04:52 PM
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Quote:
Originally Posted by alfaitalia View Post
My Jeep has a sticker under the hood warning me not to use R12 in my a.c. system .....not that you can buy it here. Not seen that sticker on any others I've looked at. Strange.

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R12 system has different size connectors so you couldn't use R134a in a R12 system or vice versa.
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post #14 of 16 Old 06-13-2015, 10:28 AM Thread Starter
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Update: went to mechanic

Mechanic flushed and refilled with R134a with dye - its now blowing cold. We will see how long it lasts, and then look for the leak. Charged me $150 for that plus an oil change.

He said that hopefully it will not need a new evaporator which he estimated at about $1200 and said would best be done by the dealer. From what I've read here on the forum, most of that cost is due to labor - taking out the whole dash.

Im hoping it will last at least til October when it starts to cool off here, then if it is the evaporator core I can decide whether or not to tackle it myself. If its just a slow leak, I will just keep adding freon.
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post #15 of 16 Old 06-13-2015, 12:35 PM
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Quote:
Originally Posted by djs99
Mechanic flushed and refilled with R134a with dye - its now blowing cold. We will see how long it lasts, and then look for the leak. Charged me $150 for that plus an oil change. He said that hopefully it will not need a new evaporator which he estimated at about $1200 and said would best be done by the dealer. From what I've read here on the forum, most of that cost is due to labor - taking out the whole dash. Im hoping it will last at least til October when it starts to cool off here, then if it is the evaporator core I can decide whether or not to tackle it myself. If its just a slow leak, I will just keep adding freon.
it's sad he is a AC repair guy and doesn't have a sniffer to tell you if the evap is leaking or not. It's a very simple task if one has the tester.

And with the exception of my Saturn every AC leak I had was the EVAP.
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