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A/C freon recharge - low side port?

A/C freon recharge - low side port?

Postby tjohnson [OP] » Jul 20 2011, 2:59pm

I have a 2002 Silverado with a 5.3L engine. The A/C is not working and I want to check the pressure on both the low and high side, but can not find the low side port. There are 2 ports (both a large and small size) on the metal line running from the evaporator to the condenser, but I can't find a port between the compressor and the evaporator, which should be the low side. Please let me know where to low side port is.
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Re: A/C freon recharge - low side port?

Postby SilverSurfer » Jul 21 2011, 3:35am

I just popped the hood on my truck to make sure. Those are your high and low side ports. The connector between them is more than just that, that's where your orafice tube goes.
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Re: A/C freon recharge - low side port?

Postby starspangled6.0 » Jul 21 2011, 3:39am

I just tried to recharge my A\C system, and Larry's right- one of the ports is high, one is low. If you buy a recharge can from the auto parts store, it will only fit on the low side, which, if I remember right, is the largest of the two fittings.
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Re: A/C freon recharge - low side port?

Postby SilverSurfer » Jul 21 2011, 3:44am

High side = big; low side = small
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Re: A/C freon recharge - low side port?

Postby SilverSurfer » Jul 21 2011, 3:58am

If you're going to add freon it's best to do this with the engine running, a/c on max and blower on high. If you have rear air, have that on full blast, too. Add to the low side and monitor high side pressure. High side pressure should be 2.2 to 2.5 times the ambient temperature. If it's 100 degrees then the high side pressure should be between 220 and 250 psi. Start by targeting the lower end of that, it's easier to add than remove.

When you stop adding your low side should be between 30 and 40 psi.
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Re: A/C freon recharge - low side port?

Postby tjohnson [OP] » Jul 21 2011, 1:09pm

Thanks for the great advice.....all of the systems I have dealt with in the past did not have the lo and hi sides on the same tube 12" apart.

Here is the full story. It is my mom's truck and a shop told her she needed an A/C compressor and it would cost $1000. I took a look at it and the belt was missing, so they couldn't know the compressor was bad. The belt broke because the idler pulley bearing seized up, a very easy and cheap fix. However the A/C still didn't work so I check the freon and it was low so I tried to add some, but it wouldn't take it from the low side, which lead to my question of where the low side was. In the process of measuring the pressure on both the hi and lo sides I discovered the hi side port was leaking so I replaced that last night and I need to get pump today to evacuate and recharge. I also have learned that it was not taking a charge from the low side because you have to short out the low side pressure switch to get the compressor to kick in. It will be 100F with high humidity for the next 3 days so hopefully a recharge is all that is required!
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Re: A/C freon recharge - low side port?

Postby PMEDIC9 » Jul 06 2012, 5:29pm

I have a 2001 silverado 5.3 and just added some 134 and the low pressure port was the smaller one and was located closest to the cab the high pressure port was closest to the front of the truck and larger in size. My truck was blowing cool but not cold in heat. I added 1/2 a can of 134 and it's blowing nice and cold now. :D
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Re: A/C freon recharge - low side port?

Postby MorpheusHusky » Jul 27 2012, 7:15pm

This is a great thread, helped me top off my 2004 Silverado, thanks guys!
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