AC Help?

[derrel]

I could not figure if this was the right place to post this or not? I just got a 2004 GMC Duramax truck. I am REAL happy so far? I have installed a 4" exhaust, Edge Juice & the Kennedy air box mod. Great stuff. My AC is not that cold though. It is a fairly low miles truck I bought from my uncle & only has 45,000 miles on it & has never had the AC looked at or anything. I have not bought the service manuals yet, they are on the list? I have done AC work on older cars R12 & R134A systems. But I have never seen both (what I think are?) the high pressure valve & low pressure valve on the same line before? It does look like there may be an orfice tube or something between them, but this sure does look strange? Does anybody have thoughts on what the guages should be reading on these sytems? I have been seeing some threads on other sights about using the temprature differential method on either the condenser or evaporator to fine tune the R134A systems? Does anybody have any experience they would like to share?

[More Power]

The low & high pressure switches are not on the same line. Typical low-side pressures cycle in the range of 22-46 psi. The high-side can reach 340+.

Is your compressor clutch engaging when it's warm outside and you activate A/C?

Is there a signficant temperature differential across the orifice?

We have an article in the subscriber archive that explains all this plus troubleshooting in detail.
http://www.thedieselpage.com/members/archive/airconditioning.htm


Jim

[derrel]

Thank You that is a great help. Although it was as I suspected that the orfice tube changes the line from high pressure to low pressure. Both fittings are within 6" of each other I have never seen that before? Not that there is much experience talking there! Thanks Again.

[DmaxMaverick]

If the fittings are close together, like yours, there will be an orifice between them. Before the orifice is high, after is low. It will look just like a coupler fitting, but there's an orifice/screen in the fitting. I've seen a few late models like this. Older models have the same type fitting with the orifice, but the schrader valves are in different locations. Same result, though.

[mattb5150]

Last summer I had an issue with my AC wouldn't get cold when outside temps were over 100 and the recirc light would flash when I tried to engage it. Then it just went away. Now I'm noticing the top hose going from the compressor to the radiator area is oily and the fan shroud is oily below the hose. Perhaps the hose is leaking and I'm losing refrigerant pressure slightly? Anyone had this issue?

Matt

[DmaxMaverick]

If the area is oily, look for other sources. Like the PS pump reservoir. If it's overfilled, or overheated, it will overflow (that's a lot of 'overs', huh?). If the oil is isolated to the compressor line and below it, you have a leak in the HP hose/line, probably at a connection (crimp or fitting), or an abraded hole somewhere. Look for places where it may have been rubbing against something. If this is the case, you would be losing freon charge. The result would be a less-than-optimal to non functional A/C system. It can also cause the lights on the control head (HVAC control) to flash and not engage certain features. The "recirc" feature will also not work and flash the light when you are in any mode of defog/defrost (even one click into it).

[madmatt]

I could not figure if this was the right place to post this or not? I just got a 2004 GMC Duramax truck. I am REAL happy so far? I have installed a 4" exhaust, Edge Juice & the Kennedy air box mod. Great stuff. My AC is not that cold though. It is a fairly low miles truck I bought from my uncle & only has 45,000 miles on it & has never had the AC looked at or anything. I have not bought the service manuals yet, they are on the list? I have done AC work on older cars R12 & R134A systems. But I have never seen both (what I think are?) the high pressure valve & low pressure valve on the same line before? It does look like there may be an orfice tube or something between them, but this sure does look strange? Does anybody have thoughts on what the guages should be reading on these sytems? I have been seeing some threads on other sights about using the temprature differential method on either the condenser or evaporator to fine tune the R134A systems? Does anybody have any experience they would like to share?

pressure varies depending on temp and humidity. yesterday here it was 85 and 75% humidity. my pressure (on a gas vehicle I was working on) was good at 38 psi and 198psi w/ a vent temp of 54*.

13-18°C (55-65°F)
0-100%
150-279 kPa (22-41 psi)
420-1140 kPa (61-165 psi)
9°C (48°F)

19-24°C (66-75°F)
Below 40%
150-298 kPa (22-43 psi)
531-1240 kPa (77-180 psi)
11°C (52°F)

Above 40%
176-366 kPa (26-53 psi)
760-1510 kPa (110-219 psi)
14°C (57°F)

25-29°C (76-85°F)
Below 35%
216-359 kPa (31-52 psi)
990-1550 kPa (143-225 psi)
15°C (59°F)

35-50%
250-382 kPa (36-55 psi)
1130-1640 kPa (164-238 psi)
16°C (61°F)

Above 50%
275-430 kPa (40-62 psi)
1230-1820 kPa (178-264 psi)
18°C (64°F)

30-35°C (86-95°F)
Below 30%
287-434 kPa (42-63 psi)
1350-1930 kPa (195-280 psi)
19°C (66°F)

30-50%
311-463 kPa (45-67 psi)
1440-2040 kPa (209-296 psi)
21°C (70°F)

Above 50%
342-506 kPa (50-73 psi)
1560-2190 kPa (226-318 psi)
23°C (73°F)

36-41°C (96-105°F)
Below 20%
366-506 kPa (53-73 psi)
1750-2300 kPa (254-334 psi)
23°C (73°F)

20-40%
382-531 kPa (55-77 psi)
1800-2390 kPa (261-347 psi)
25°C (77°F)

Above 40%
409-557 kPa (59-81 psi)
1900-2480 kPa (276-360 psi)
27°C (81°F)

42-46°C (106-115°F)
Below 20%
452-575 kPa (66-84 psi)
2180-2660 kPa (316-386 psi)
27°C (81°F)

Above 20%
465-599 kPa (68-87 psi)
2220-2730 kPa (322-396 psi)
29°C (84°F)

47-49°C (116-120°F)
Below 30%
535-629 kPa (78-91 psi)
2580-2900 kPa (375-421 psi)
30°C (86°F)

[mattb5150]

Okay, it did it again the other day, temps went over 100 and the AC worked, but not very cold. The upper hose has a small cut in it where it is held onto the fan shroud by a plastic clip. The clip was hiding the cut until I pulled the hose out of it and cleaned off the oil. I am betting when the temps get up the pressure builds and forces the freon and oil out in very small amounts. Question, which hose is that, partszoneonline lists an accumulator hose and a condenser hose? Am I to assume that is the condenser hose since it runs from the compressor to the radiator area?

Thanks, Matt

[DmaxMaverick]

Okay, it did it again the other day, temps went over 100 and the AC worked, but not very cold. The upper hose has a small cut in it where it is held onto the fan shroud by a plastic clip. The clip was hiding the cut until I pulled the hose out of it and cleaned off the oil. I am betting when the temps get up the pressure builds and forces the freon and oil out in very small amounts. Question, which hose is that, partszoneonline lists an accumulator hose and a condenser hose? Am I to assume that is the condenser hose since it runs from the compressor to the radiator area?

Thanks, Matt

Correct. The "condenser hose" goes from the compressor to the condenser (radiator area). The "accumulator hose" goes from the accumulator to the compressor (usually larger of the two). The "compressor hose" is the high pressure line, and could/would leak more in hotter weather, like you suspect, with higher pressures. The hose can be repaired, if it is in good condition otherwise, and space allows a coupler. Much less expensive than a new line.

[mattb5150]

I had a local garage discharge the freon when I had my truck in to have them replace the steering shaft. I installed a new compressor hose from partszoneonline and now need to recharge the system. I was originally going to have the shop that discharged it, recharge it. Was wondering if I should just get the cans from WalMart and do it myself. If I choose this route can anyone tell me how much the system needs? They carry 18oz. cans that include the oil and refrigerant.

Matt

[spongebob]

I had a local garage discharge the freon when I had my truck in to have them replace the steering shaft. I installed a new compressor hose from partszoneonline and now need to recharge the system. I was originally going to have the shop that discharged it, recharge it. Was wondering if I should just get the cans from WalMart and do it myself. If I choose this route can anyone tell me how much the system needs? They carry 18oz. cans that include the oil and refrigerant.

Matt

matt, get a licenced contractor to do it for you..you could damage your system and hurt yourself.
it wont cost that much..
if you insist..there should be a lable somewhere with the amount of the freon it takes..

[rat4go]

The system needs to be evacuated before you can recharge it. Unless you do this, you'll have air in the system with the R134a and you'll just be wasting your $ at walmart buying cans of R134A, then posting again that the system isn't any better. A good shop will pull a vacuum on the system for you, then let it sit for 15-20min to see if it holds vac. If it doesn't, you still have a leak that needs fixin' before you waste $ on a R134A charge. The other thing to consider is that most of the 'cans' of R134A have oil mixed with the R134. You probably don't need more oil in the system unless you had a big 'all of a sudden' leak that sneezed the oil out. More oil is not necessarilly better.

Good luck!

[madmatt]

not only do most contain oil but often times have some sort of sealant or stop leak in the which damage A/C equipement and over time can mess up sensors. Let a shop do it. I do it in my garage w/ the cans but use my vaccum pump the evac the air from the system first.

[spongebob]

listen to mat and rat...
auto stores shouldnt sell those cans in the store..

very dangerous

[mattb5150]

Will have it done at shop. Thanks for replys!

Matt