AC Problems

GMCTodd · April 23, 2005

My 2002 GMC Sierra Crewcab AC works great until it gets in traffic then it blows hot air. It also does this at idle in th garage. The dealer replaced the compressor, controls, high pressure switch and it still does it. The compressor is being shut off by the high pressure switch. If you put gauges on the low port the pressure will climb high and the air starts blowing hot. After taking it in to the dealer the 3rd time they put a fan behind the grill. This helped but it is really really noisy and very annoying. I put in a new heavy duty fan clutch and it works well without the electric fan unless the temp gets above 80 (when you need the ac) This truck should not need an auxillary fan, the dealer even said so, but that is all that they could find that would help. Is there any suggestions out there??

redvett · April 24, 2005

My 2002 GMC Sierra Crewcab AC works great until it gets in traffic then it blows hot air. It also does this at idle in th garage. The dealer replaced the compressor, controls, high pressure switch and it still does it. The compressor is being shut off by the high pressure switch. If you put gauges on the low port the pressure will climb high and the air starts blowing hot. After taking it in to the dealer the 3rd time they put a fan behind the grill. This helped but it is really really noisy and very annoying. I put in a new heavy duty fan clutch and it works well without the electric fan unless the temp gets above 80 (when you need the ac) This truck should not need an auxillary fan, the dealer even said so, but that is all that they could find that would help. Is there any suggestions out there??

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My guess is that if the condenser is clean than i would look at too much pag oil in the system. Has the compresser been changed more than once? Did the dealer put a full load of oil in the compresser? If so there is too much in the system causing poor cooling. The system must not have more than the prescribed amount of oil.

GM-Tech · April 24, 2005

Are you sure it's a high pressure problem and not the low pressure (cycling) switch? We have replace those by the score!

If your pressure cycling switch has a brown band around the black plastic portion of the switch, it's definitely the one that's been a problem. The pressure cycling switch is the one that is screwed onto the accumulator (the silver can near the firewall).

BBSilverado · April 24, 2005

check your pressures and compare it to this GM chart.

GMCTodd · April 28, 2005

I took it into the dealer again. I will see what he has to say.

snoman · April 28, 2005

I took it into the dealer again. I will see what he has to say.

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Yes check low pressure cut out switch too. Bear in mind that you have to get air through raditor/condensor stack to cool freon (R134a) to be able to provide cool air and sometime it can take some agreesive fans to do that, especaily with a diesel (if you have one) because of the extra resistance in the stack from condensor, intercooler and then thick radiator and sometimes it takes some fan noise to maintain good airflow. Make sure that all the the cores are clean of any possible blockage too to get maximum possible airflow.

GMCTodd · May 1, 2005

It was not hot enough here for the dealer to get it to act up again. They have replaced every switch and they said they checked the condensor again. It already has a new fan clutch and an extra electric fan that they mounted to blow air through the condensor, so it has plenty of air flow. If it is above 80 deg outside and you slow down in traffic the ac starts blowing 80 deg air and will not start blowing cold again until 20 minutes of going fast again. Also if it is close to 90 deg outside at idle it will start blowing 70 deg air. I told the manager what "redvett" said about to much PAG oil in the system. He said that the new compressor comes with the right amount of oil already in it, but he did say there is a chance they did not get all of the old oil out. When it gets hot here again in a week or two I will take it back in to them. If he remembers about the pag oil thing he may flush out the system and put in the correct amount...

redvett · May 1, 2005

It was not hot enough here for the dealer to get it to act up again. They have replaced every switch and they said they checked the condensor again. It already has a new fan clutch and an extra electric fan that they mounted to blow air through the condensor, so it has plenty of air flow. If it is above 80 deg outside and you slow down in traffic the ac starts blowing 80 deg air and will not start blowing cold again until 20 minutes of going fast again. Also if it is close to 90 deg outside at idle it will start blowing 70 deg air. I told the manager what "redvett" said about to much PAG oil in the system. He said that the new compressor comes with the right amount of oil already in it, but he did say there is a chance they did not get all of the old oil out. When it gets hot here again in a week or two I will take it back in to them. If he remembers about the pag oil thing he may flush out the system and put in the correct amount...

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Snoman,

We at (GM) had this problem often when a customers vehicle had the compresser changed. The service person must drain the old compresser and measure the remaining oil and also if the new compresser has oil drain and add only the amount in the old compresser.

If they didnt do this you have too much oil. Have them remove & flush the condenser and only add the amount oil for your vehicle. Also has the orfice tube been changed?

snoman · May 1, 2005

It was not hot enough here for the dealer to get it to act up again. They have replaced every switch and they said they checked the condensor again. It already has a new fan clutch and an extra electric fan that they mounted to blow air through the condensor, so it has plenty of air flow. If it is above 80 deg outside and you slow down in traffic the ac starts blowing 80 deg air and will not start blowing cold again until 20 minutes of going fast again. Also if it is close to 90 deg outside at idle it will start blowing 70 deg air. I told the manager what "redvett" said about to much PAG oil in the system. He said that the new compressor comes with the right amount of oil already in it, but he did say there is a chance they did not get all of the old oil out. When it gets hot here again in a week or two I will take it back in to them. If he remembers about the pag oil thing he may flush out the system and put in the correct amount...

<{POST_SNAPBACK}>

Snoman,

We at (GM) had this problem often when a customers vehicle had the compresser changed. The service person must drain the old compresser and measure the remaining oil and also if the new compresser has oil drain and add only the amount in the old compresser.

If they didnt do this you have too much oil. Have them remove & flush the condenser and only add the amount oil for your vehicle. Also has the orfice tube been changed?

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Yes too much oil can cause this problem as can a bad expension valve but given the frequency of the problem in trucks that have never been serviced since factory that means that either they got to much oil on day one, have a expansion valve/orfice the is too large or the condensor is not cooling the "freon" enough to remove enough latent heat for it so that it expands and cools properly. The theory they work on is really pretty simple and any of the above (as well as a bad compression or plugged screen in orfice or receiver/dryer) can cause lack of cooling but if they are all within designed specs and insufficant air is moved through the condensor core, the cooling will lack capacity.