Dodge Durango air conditioner diagnostics

[Hannibal]

I'm hoping some of the membership here can help me figure out what the cause of an underperforming air conditioner is.
Vehicle is an 01 Dodge Durango, 4.7 V8 with the dual climate controls and split heater/evaporator behind the back seat. The issue is, air conditioner compressor comes on, runs continuously, but does not cool well at all.
We bought this vehicle used a few years ago, and it appeared that the compressor had been replaced, but I'm not certain. I do know that the electric fan was bad and the engine driven fan clutch was also not working correctly, so I replaced them both.
It was low on refrigerant, so I added a couple of cans and it worked fine. Every spring I'd have to add refrigerant, and often a bit more in late summer.
This spring I was moving and when the A/C wasn't working, I presumed it needed refrigerant again. I noticed it wasn't as low as usual, and it never did work very well at all. So. Apparently, low refrigerant isn't the cause this time.
As I stated, cooling performance is very poor both from the front vents and from the vents from the rear also. My understanding is there are 2 expansion valves on this system, so I'd not think both have gone bad, but air conditioning is not my specialty.
As I recall, the low side pressure on a 95 degree day was about 42 PSI. I did not check the high pressure side, so I don't know what it was.
My questions are, what should my low and high pressures be on a 90 degree day? How can I determine if the compressor or expansion valves are bad? Is it possible something else is restricting flow? If so what do I need to look for.

The high pressure side from the compressor is not near what I would call hot, and the return side is not nearly as cold as I normally find.

If anyone can tell me where to start checking, I'd be quite greatful.

Thanks in advance.

[bullet maker 57]

According to the chart, at 95 degrees your high side should be 114 psi. Need to know what the discharge air temp is to figure out low side pressure.

[Hannibal]

High side 114?

Wow. Thought it was supposed to be a lot more than that. Ok, I'll hook the gauge set back up tomorrow and see what's going on.

I used to have a digital thermometer. Guess I'll have to see about buying one. . . .

[kens]

no way 114psi on 95 degree day.
as a matter of fact, I'll dispute 114psi on any day you need a/c.
R134 runs at a much higher pressures than the old school R12.
On a 95' day, R134 high pressures are at or near 300psi.

[Hannibal]

no way 114psi on 95 degree day.
as a matter of fact, I'll dispute 114psi on any day you need a/c.
R134 runs at a much higher pressures than the old school R12.
On a 95' day, R134 high pressures are at or near 300psi.

That's more along the lines of what I was thinking, but as I said in the opening post, I am NOT an air conditioning guy.

Anyway, I'll check pressures tomorrow and post them here. Should have already done that it appears.

[454 shooter]

The air conditioner in my van was not preforming well because it had to much refrigerant in it. "little do'em, good much do better" is not always true

[Hannibal]

The air conditioner in my van was not preforming well because it had to much refrigerant in it. "little do'em, good much do better" is not always true

You've no idea how much I hope this is just a stupid mistake I've made.

[Finster101]

High is going to run 225-250 psi low side 35-50 depending on outside temps. An over charged system will perform poorly, also verify you have good air flow over the condenser.

[rancher1913]

don't forget to replace the cabin filter, may help with airflow.

[Hannibal]

Well, I owe everyone an apology. I put the gauges back on today, and had about 10 PSI on the low side and 90 or so on the high side.
I'm not sure how I managed to confuse myself so thoroughly, but 36 ounces later, and I had 35 psi on the low side and 180 on the high side. System capacity is 2.44 lbs. It's cloudy, high humidity and 78 degrees here today, so I'll check it again another day. Discharge air was 51 degrees, so I'm going to have to find and fix the leak or this will apparently be a nagging issue.

I guess that's what happens when a guy gets in a hurry and isn't paying enough attention. Thanks to all who replied. Sorry for the misinformation.

[Finster101]

I find it a bit ironic that as a licensed auto tech I and the shop I work for can be fined heavily for venting Freon or charging leaking systems yet anyone can go to autozone and by recharge kits and just keep dumping it in to leaking a/c systems.

[Hannibal]

I find it a bit ironic that as a licensed auto tech I and the shop I work for can be fined heavily for venting Freon or charging leaking systems yet anyone can go to autozone and by recharge kits and just keep dumping it in to leaking a/c systems.

Lots of hypocrisy at the EPA. No arguing that. I find it interesting that you refer to it as 'Freon' as well.

If it makes you feel better, I do intend to find and fix the leak.

[Three44s]

I find it a bit ironic that as a licensed auto tech I and the shop I work for can be fined heavily for venting Freon or charging leaking systems yet anyone can go to autozone and by recharge kits and just keep dumping it in to leaking a/c systems.

Well, I had the JD dealership come out and do just that, finish off my compressor and attempt to bill me over 1K back in the early 90’s to my swather. And .... that was with R12!

And so began my school of hard knocks education with AC.

Our biggest challenge with off road ac is dirt. I realize the OP is working on a truck but even household systems plug up over time so on road units are not immune to the problem.

I realize you can have a leak from pressure that vacuum will not be lost in but I evacuate my stuff for 24 hrs or more and achieve 28 1/2” of Hg. Turn my pump off find my draw down right where I left it after being off over night. If I am dubious about the repair I can also pre-charge with dry nitrogen to a given pressure and lock it down for an adequate amount of time before I evacuate. I have been known to borrow a detector and sniff it out. That does no good though if it is inside an internal passage way in the cab however.

A few years ago I pulled all the original hoses and had a specialty radiator shop whittle me new ones. Lots of piece of mind.

Best regards

Three44s

[EDG]

A good leak detector will find an evaporator leak by detecting refrigerant inside the cab. If you stick the wand into a vent turn off the fan first. Some detectors have a filament that can be damaged by the high velocity air pressure.
When your AC is shut down and equalized the pressure on the low side (evaporator) is higher making finding refrigerant in the cab easier.
If your system worked well for years an developed a slow leak suspect a tiny hole in the evaporator caused by corrosion.
The chemistry of refridgerants includes fluorine. Fluorine will react with any molecules of moisture to form hydrofluoric acid which will attack everything in the system. It will attack the thin aluminum evaporator eating holes in it.
The best cure is to purge the system and evacuate it down to a hard vacuum several times. You cannot let any moisture into the system even from the service hoses and gages. So you need to vacuum out the gage set and purge it with refridgerant too. If you achieve a system as dry as the back side of the moon your AC will live a long leak free life.

My AC education came before there was an internet from an official GM shop manual for my mom"s 1973 Impala. Along the way I have replaced many evaporators that eventually developed pin holes from factory and service technician charges. Because I use a better more through process to purge and evacuate the system I have never had to replace any evaporator that I have installed.
The service specs for automotive systems say to pump the system down to at least 50 microns or less. My old vacuum pump is a Centech laboratory pump capable of .3 microns. That is point 3. It is slow but very capable of producing better vacuum than used by the factory or service techs. I typically pump a system down and hold it for 30 min. Then a tiny bit of refrigerant is allowed to equalize the system to a few PSI. This purge gas dilutes and mixes with any aire and moisture molecules. Then the system is pumped down and purged 2 more times. Finally my lab pump is allowed to pump for an hour and is shut off to check for leaks.
All this pumping is done with the fill hose connected to a can so the line is evacuated too. When the can valve is opened it goes straight into the hose under vacuum. There is NO way for any moisture to be let in. Successive cans are installed by allowing a tiny leak at the can tap back out of the partially charged system. In this way you always have positive refrigerant pressure preventing air from entering the hoses and gauge assy.
This makes for a longer vacuum but much more satisfactory evacuation process. The result is no internal corrosion and very long system life.

Well, I had the JD dealership come out and do just that, finish off my compressor and attempt to bill me over 1K back in the early 90’s to my swather. And .... that was with R12!

And so began my school of hard knocks education with AC.

Our biggest challenge with off road ac is dirt. I realize the OP is working on a truck but even household systems plug up over time so on road units are not immune to the problem.

I realize you can have a leak from pressure that vacuum will not be lost in but I evacuate my stuff for 24 hrs or more and achieve 28 1/2” of Hg. Turn my pump off find my draw down right where I left it after being off over night. If I am dubious about the repair I can also pre-charge with dry nitrogen to a given pressure and lock it down for an adequate amount of time before I evacuate. I have been known to borrow a detector and sniff it out. That does no good though if it is inside an internal passage way in the cab however.

A few years ago I pulled all the original hoses and had a specialty radiator shop whittle me new ones. Lots of piece of mind.

Best regards

Three44s

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