AC Not blowing COLD and Compressor cycling off and on

My car is a weekend cruiser, 2004 with 21k miles. Kenne Bell supercharged. Don’t really use the AC but last summer being the first summer I owned the car I wanted to run it just to get the system running. Seemed to work fine. Well I went to use it the other day and was blowing hot. So I figured needed a charge. Put AC Pro gauge on the system today and noticed compressor cycles on and off way to frequently. And the gauge shoots all the way up and then the compressor turns off and gauge goes to 0 then kicks back on and starts shooting back up again heading toward the red. I replaced the ac clutch cycling switch near the firewall and same thing happening. What could it be??


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haven't played with AC in a LONG time but google the pressures for our cars. It may be hitting the limit and shutting down.

Sounds like a pressure issue to me as well. Did you try bypassing the pressure switch just to see what happens?

When compressors kick on the pressure should start going down. Then when compressor kicks off the pressure will rise again. Your stating it's doing the opposite correct?

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2003SVTFreak said:

When compressors kick on the pressure should start going down. Then when compressor kicks off the pressure will rise again. Your stating it's doing the opposite correct?

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Click to expand...

I’m not sure now. You maybe right


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slo984now said:

Sounds like a pressure issue to me as well. Did you try bypassing the pressure switch just to see what happens?

Click to expand...

When you say bypass the pressure switch are you referring to the switch I described I replaced? And if so just unplug the wire connector?


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You are low on coolant. This results in the compressor cycling on/off with no cold air.

If what I'm saying is correct then you are low on freon and have a small leak. Sometimes thays caused from.lack of use. Get a can and fill slowly stopping every 2 second and rechecking pressure. Pressure should at 35lbs at idle when AC compressor is on.

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I will try to add some and see. I got nervous Bc I went to add and was reading so high on AC Pro gauge I didn’t want to overfill. But you guys are saying the gauge could be going crazy like that do to the cycling off and on Bc of low Freon


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Goose17 said:

You are low on coolant. This results in the compressor cycling on/off with no cold air.

Click to expand...

Goose is right about the charge but you should always check your condenser for air flow as well

Make sure fan is kicking on.

And put your A/C on max, recalculate, and the blower on high when checking and charging.

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Its been awhile since I played with or charged an AC system, but isn’t there a high pressure and a low pressure side...? Are you checking the correct side?

Goose17 said:

Its been awhile since I played with or charged an AC system, but isn’t there a high pressure and a low pressure side...? Are you checking the correct side?

Click to expand...

You are correct Goose.

2003SVTFreak said:

If what I'm saying is correct then you are low on freon and have a small leak. Sometimes they are caused from lack of use. Get a can and fill slowly stopping every 2 second and rechecking pressure. Pressure should at 35lbs at idle when AC compressor is on.

Click to expand...

^^^ This.....And as Goose mentioned make sure you check that 35lbs on the LOW side of the system. The LOW side is also where you add the Freon.

I highly recommend you rent an A/C gauge set (Also known as a manifold set) from your local auto parts store. They look like this:



Make sure you do not over fill your system. Too much Freon is as bad as too little. Also, check your system and make sure everything seems in order. Make sure your condenser is clean and free of debris. Lastly, watch a YouTube video on how to charge your A/C.

You CAN do this job, but you need to know what your doing or you can damage your system.

From what I remember, I second gooses online diagnosis. Rapid compressor cycling and warm/hot air is a classic sign of low Freon. Get it professionally evacuated and vacuumed tested and have it refilled with some dye in the Freon so if there is a leak you can find it with a black light and repair it.

i do refrigeration work for a living-

no need to evacuate at this point. adding some r134a with a uv dye/oil charge should suffice for the time being. once you locate the leak and replace the offending part(s), go ahead and have it evacuated and properly charged. there is no exact pressure to charge to...you can either weigh in the proper charge, or know enough to be able to "rule of thumb" your way to a "good enough" charge. the temperature inside and outside the car will affect the low side pressure you see on the gauge.

on cars, the low side and high side have different sizes of access fittings...it's impossible to hook up to the wrong one.

Well I added the bottle of AC Pro and while doing so the compressor finally started acting right and I was finally able to get a reading. After full bottle added it was reading on the low side abt 20. Noticed air blowing much colder. I will wait until next time I use the car on a nice hot day and then re check level and see. Probably going to need some more.


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