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How Do I "properly" Recharge A/c On A 2003 Sierra


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#1 glasses97

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Posted 18 April 2010 - 08:53 AM

Does anybody know how to measure the superheat on a 2003 gmc sierra? Going off of the low pressure gauge is not a good way to do it as there are many variables to screw the measurement up. The service manual simply states "The J 43600 is a complete air conditioning service center for R-134a. The ACR 2000 recovers, recycles, evacuates and recharges A/C refrigerant quickly, accurately and automatically.

This tells me that gmc does not even have a procedure for people to check the superheat and that they go on the weight of the refrigerant charge. There must be a procedure out there somewhere for checking the superheat!

Thanks

#2 Wires

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Posted 18 April 2010 - 10:31 AM

Does anybody know how to measure the superheat on a 2003 gmc sierra? Going off of the low pressure gauge is not a good way to do it as there are many variables to screw the measurement up. The service manual simply states "The J 43600 is a complete air conditioning service center for R-134a. The ACR 2000 recovers, recycles, evacuates and recharges A/C refrigerant quickly, accurately and automatically.

This tells me that gmc does not even have a procedure for people to check the superheat and that they go on the weight of the refrigerant charge. There must be a procedure out there somewhere for checking the superheat!

Thanks



If you have a set of gauges to monitor the high/low pressure you should be able to do it. Used to do it a lot on R12 vehicles, and I don't think anything (other than the freon type) has changed since then. All cooling systems are the same.

#3 pm26

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Posted 18 April 2010 - 10:42 AM

You can rent a set of gauges and a good vacuum pump from Auto Zone for free (with a refundable deposit). The key to properly recharging the system is to make sure you pull adequate vacuum on it to remove the moisture. make sure you have sufficient refrigerant oil in the system. R134 systems are more sensitive to the correct amount of refrigerant than the old R12 systems. For a rule of thumb, keep charging the system until you see the low side pressure around 25-35 psi, and the system switching the compressor back on when the pressure drops to about 25psi. The high side pressure can be anywhere from 300 to 350 psi.

Do you have an expansion valve/receiver-dryer system or a fixed orifice/accumulator system? In the former, the compressor clutch does not cycle.

If you are replacing the A/C compressor, also replace the expansion valve or orifice tube, and the receiver-dryer or the accumulator. If the new compressor has no oil in it, add about 4 oz of proper viscosity refrigerant PAG oil to it, then manually turn the compressor shaft by the clutch center bolt in the clockwise direction about 12 times, tilting the compressor 3with the clutch down so that the compressor seal gets lubricated. Another 4 oz of oil is added to the receiver-dryer or the accumulator. There should be about 8 oz total of refrigerant oil in the system.

If your old compressor failed catastrophically and there are metal shavings in the system, the system should be flushed first.

#4 thedan42487

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Posted 18 April 2010 - 11:57 AM

question, why are you recharging your system? changing compressor or something?

04 sierra ext. cab, no emblems, level kit, 33" bfg's, flowmaster exhaust, k&n intake, line-xed bedliner and running boards

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#5 glasses97

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Posted 18 April 2010 - 08:58 PM

Thanks for the responses; however it is not as specific of info that I am looking for. I have gauges and a vacuum pump. The reason I have to recharge is that I had a leak at a fitting. I dumped some stop leak in and now have no more leaks. The problem with using straight pressure measurement to fill the system is that it can be substantially over or under charged depending on ambient temp, air flow, evap temp, and condenser temp. This truck has a fixed orifice, that is why I was asking about the superheat. The manufacture uses weight to determine the proper charge, what I want to do is top up the system without evacuating it totally. There has to be a way to determine the correct charge using temperature measurement in conjunction with the pressure.

#6 dewfpo

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Posted 18 April 2010 - 09:24 PM

This is what has worked for me in the past with R134a systems.

Stick a temp probe in the center dash vent and turn the A/C on and fan on high, add R134a to the low side until the temp stops dropping at the center vent. At that point I stop adding refrigerant and I'm done. It's worked fine for me on many different types of vehicles.

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