2006 GMC Sierra

[JYarber]

06 Sierra 3500 Duramax. Are the online R134 PSI charts accurate? Just trying to perfect my AC as best as I can on fairly new parts replacements. Today was 95* (felt like 102*) and 40% Humidity. My PSI at idle was 45/ 300. At 1700ish RPM idle they were about 30/220. AC vent thermometer at raised 1700ish idle was reading about 50* and regular idle about 55*.

[event3horizon]

50's is not bad at all to be honest. Yea, a fantastic system will do 40-45 at the vents but with an older system like that, 50's is to be expected I'd think.

[JohnHere]

Reading pressures at idle don't reveal much of anything. At ~1,700 RPM, the pressures look very good, yet the vent temperatures are rather warm-ish. Are you sure you don't have any reheating going on—that is, heated air mixing with the cooled air?

Did you replace the cabin air filter, if it has one? Did you also examine and replace the OT? What did the old OT look like when you pulled it out?

The refrigerant specifications for your truck mirror those that I have.

I generally don't put too much stock in P/T charts because they can often be misleading.

[JYarber]

Sorry for the late reply. My truck doesnt have a cabin filter but will be actually adding one to it. Unfortunately my Denso compressor died this week and waiting on a replacement now. Since it failed I have flushed all the lines out, replaced the drier and orifice tube. Plan to add 7oz of PAG 46 to the system and 1.6lbs of freon and see where everything is at on the manifold set. I know in the past recently a little over 1.5 cans (12oz cans) would have my pressures around 300 on the high side at idle so I always stopped adding freon as I didnt want to overcharge it. I even had the PRV on back of compressor vent one day after a recharge. Makes me wonder how am I supposed to get the required 1.6lbs in it when that happened with less than 1.6lbs in it?

Reading pressures at idle don't reveal much of anything. At ~1,700 RPM, the pressures look very good, yet the vent temperatures are rather warm-ish. Are you sure you don't have any reheating going on—that is, heated air mixing with the cooled air? What are P/T charts?

Did you replace the cabin air filter, if it has one? Did you also examine and replace the OT? What did the old OT look like when you pulled it out?

The refrigerant specifications for your truck mirror those that I have.

I generally don't put too much stock in P/T charts because they can often be misleading.

[JohnHere]

Did the previous compressor fail in such a way that it sent metal and plastic debris downstream? If so, then you'll also need to replace the condenser.

The specs I have for your truck call for 8.0 fluid ounces of PAG-46 with a Denso compressor. You should pour-out whatever oil comes in the new compressor and figure your total estimated oil amount on the system as it currently stands. If you're not replacing the evaporator, it probably will retain about 1.5 ounces of oil. If you replace the condenser, you'll need to add about 1.5 ounces of oil to the new one, as well as to the new R/D, for a total of about 4.5 ounces now in the system. The rest of the oil, about 3.5 ounces, should then be added to the now-empty new compressor.

The system should easily take all 25.5 ounces net weight (1.6 pounds) of refrigerant when charged into a well-held vacuum (by weight), and the compressor should engage shortly after achieving positive system pressure. If it doesn't, then something else is wrong—possibly with a pressure switch or with your charging set-up. We've already ruled out a clogged OT as the source of the high pressure because you already replaced it.

[JYarber]

Did the previous compressor fail in such a way that it sent metal and plastic debris downstream? If so, then you'll also need to replace the condenser.

The specs I have for your truck call for 8.0 fluid ounces of PAG-46 with a Denso compressor. You should pour-out whatever oil comes in the new compressor and figure your total estimated oil amount on the system as it currently stands. If you're not replacing the evaporator, it probably will retain about 1.5 ounces of oil. If you replace the condenser, you'll need to add about 1.5 ounces of oil to the new one, as well as to the new R/D, for a total of about 4.5 ounces now in the system. The rest of the oil, about 3.5 ounces, should then be added to the now-empty new compressor.

The system should easily take all 25.5 ounces net weight (1.6 pounds) of refrigerant when charged into a well-held vacuum (by weight), and the compressor should engage shortly after achieving positive system pressure. If it doesn't, then something else is wrong—possibly with a pressure switch or with your charging set-up. We've already ruled out a clogged OT as the source of the high pressure because you already replaced it.

Glad you chimed in. I searched online for oil capacity and saw both 7 and 8oz listed on online sources. Any sites you use for information purposes like that?

[JohnHere]

It's a proprietary database from which I gleaned the 8.0 fluid ounces of PAG-46 for your truck. But AllData and Mitchell's reportedly have the same information. Last time I looked, you can purchase a short-term subscription to either one for just about any vehicle. They are the same factory sources that professional mechanics use and rely on.

Or you could just split the difference and make it 7.5 fluid ounces in total, which would be slightly too much or slightly too little, depending on how you look at it. IMHO, this amount would be acceptable since the difference is only a minuscule 0.5 ounce.

[JYarber]

It's a proprietary database from which I gleaned the 8.0 fluid ounces of PAG-46 for your truck. But AllData and Mitchell's reportedly have the same information. Last time I looked, you can purchase a short-term subscription to either one for just about any vehicle. They are the same factory sources that professional mechanics use and rely on.

Or you could just split the difference and make it 7.5 fluid ounces in total, which would be slightly too much or slightly too little, depending on how you look at it. IMHO, this amount would be acceptable since the difference is only a minuscule 0.5 ounce.

Ty for the help!

[JYarber]

It's a proprietary database from which I gleaned the 8.0 fluid ounces of PAG-46 for your truck. But AllData and Mitchell's reportedly have the same information. Last time I looked, you can purchase a short-term subscription to either one for just about any vehicle. They are the same factory sources that professional mechanics use and rely on.

Or you could just split the difference and make it 7.5 fluid ounces in total, which would be slightly too much or slightly too little, depending on how you look at it. IMHO, this amount would be acceptable since the difference is only a minuscule 0.5 ounce.

2-3 issues I am having that I would like your opinion on. Replaced all the parts a few weeks ago. Got the system vacuumed and recharged to the full required amount. AC was performing great. However on 2 separate occasions now if I park the truck in direct sunlight where temperatures under the hood rise from sitting all day when I first crank the truck the relief valve on the compressor has popped and vented off freon on 2 separate occasions. I have not checked the pressures since this happened but obviously it will have lower amount of refrigerant then required now.

Other issues I have noticed are sitting idle my AC is colder versus driving down the road and also it is colder on a lower fan speed versus max fan. Thanks in advance!

[Cusser]

Other issues I have noticed are sitting idle my AC is colder versus driving down the road and also it is colder on a lower fan speed versus max fan.

I can comment only on this part. It is normal for the air at the vents to be at a lower temperature at lower blower fan speeds because the air has more "time" to shed its heat to the evaporator.

Cooling of the occupants is a complex combination of vent temperature, vent air speed, direction of the vent air, how much heat soak was built up in seats/dash/etc......