Help, It's hot out!

Hello All,
I need some info on the air-conditioning in my 1999 K1500 pickup. I placed one of the cheep gauges on the low side of the system, says I need more
Freon. Stands to reason as it's only blowing cool not cold air. I put a couple of cans of R134a in and the gauge seams satisfied. How ever the air has gotten only a little cooler, but still not cold.
My question, is there anything that I can do with out having the correct equipment to the AC unit to get cold air out of it? Or should I just take it in to my friendly neighborhood Chevy dealer to be evacuated and charged?
Thanks Brian
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Hi Brian I wouldn't put any more freon in it without monitering the high side as well. Did you check your heater controls? Lots of time the doors leak and hot air is mixing with the cold AC and the result is warm air. A truck I had did that, and since I couldn't get at the heater doors, I rigged up a bypass on the heater hoses....it worked great. (Wasn't a Chevy, tho....) Might check your Condenser for cleanliness, too. Good Luck Pete

it
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I have looked at the condenser, it's clear of obstructions. I believe the heater controls are OK as when on cold and the blower is on with the AC off, I get room temperature air and it gets hotter as you increase the temperature.
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NEVER work on an AC system without the proper equipment.
The proper equipment can be had for about $80. $70 for the manifold and hoses at Autozone, and $9 for the vacuum pump at Harbor Freight <assuming you have an air compressor... little more if you don't>.
This system requires proper pressures to work properly. It all comes down to the thermodynamic law of partial pressures and pressure/volume.
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If you made the gauge happy at idle, you may still have too little R134a in there now as pressure decreases as RPM increases. Check low sides at 2k RPM (normal cruising RPM) at full operating temp, after you've had it on MAX A/C for at least 10 minutes. The compressor should cycle several times per minute as the low-sides hit cut-off for a few seconds, hence cycling the compressor.
You really can't do it correctly w/o monitoring both high and low sides, but this will get you started.
Doc

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Thanks Doc I'll see what the gauge reads at a higher engine speed.
Brian
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"'Doc'" wrote:
> > > Hello All, > > > > I need some info on the air-conditioning in my 1999 K1500 > pickup. I placed > > one of the cheep gauges on the low side of the system, says > I need more > > Freon. Stands to reason as it's only blowing cool not cold > air. I put a > > couple of cans of R134a in and the gauge seams satisfied. > How ever the air > > has gotten only a little cooler, but still not cold. > > > > My question, is there anything that I can do with out having > the correct > > equipment to the AC unit to get cold air out of it? Or > should I just take > > it in to my friendly neighborhood Chevy dealer to be > evacuated and > > charged? > > > > Thanks > > Brian > > If you made the gauge happy at idle, you may still have too > little R134a in > there now as pressure decreases as RPM increases. Check low > sides at 2k RPM > (normal cruising RPM) at full operating temp, after you've had > it on MAX A/C > for at least 10 minutes. The compressor should cycle several > times per > minute as the low-sides hit cut-off for a few seconds, hence > cycling the > compressor. > > You really can't do it correctly w/o monitoring both high and > low sides, > but this will get you started. > > Doc > > > > > >
He really needs a full pressure check here (hi and low side) and the low side can be normally 25 to 50 PSI depending on tempature and humidity and highside for 150 to 225 or so (it can spike higher on startup though) again depending on temp. GM systems "generally run on about a 6 to 1 ratio (give or take) low to high and chrysler tend to be a bit higher in ratio. (my wife Cherokee runs at about a 8 to 1 ratio when it cools the best) WHen you charge it to much, the low side will start climbing faster and it will tend to be unsteady to at a constant engine speed and cooling load as the freon never fully flashs properly and consistanly in a overcharge. Charge without proper gages can lead to trouble and if you are not really sure of what you are doing, you should seek help because you can do more harm than good with a good understanding of the pressure curves of R134a related to tempature.
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Follow up:
I checked the pressure again as Doc suggested. It shows low so I added more R134a and I have cold are now. Thanks Doc.
Brian
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Not a problem bud, glad to help.
Doc
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Doc-
working on my AC now. Finally got my own setup. what do I want to monitor, all told?
If you've already presented this info, please point me in a direction of a date or so, that it was posted.
Thanks!
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To do it right you need to monitor high and low sides (more specifically the ratio between the two), although I admit I've filled several successfully using just the low side pressures. If it's an old r-12 system converted over to 134a, you'll want to add a high-side pressure cut-off wired inline with the compressor +12V feed.
GM low-side switches cut-off at 26psi or so. You'll want low-side pressures to dip below 26 psi a few times per minute (hence cycling the compressor) at 2k RPM, max A/C, vehicle at full operating temp on a hot-as-balls day. This usually equates to around 40psi low-side at idle RPM.
Drop me an e-mail off group if ya need more.
Doc
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