Engine Size: 7.3
Refrigerant Type: 134a
Ambient Temp: 105
Pressure Low: 48
Pressure High: 220
The Excursion does not get driven much but it will be driven more real soon so I wanted to get the ac figured out. Everything was replaced a couple of years back (except for the front evaporator) and I also upgraded to a parallel flow condenser . I cleaned the lines thoroughly and oiled the system (14oz). Pulled a vacuum for an hour and then charged the 4.25 lbs of 134 as the sticker suggested on the bulkhead. The ac was never that good and I noticed that the high side was normal but the low side was higher than what I usually see on a single system car. I recovered the 134, installed a smaller orifice tube for the front, next size down, so that I could try to get the low side down with the high side maybe the same or a tad higher. Didnt work for cooling and the pressures only very slightly changed. Since the repairs Ive noticed that one of the O rings for my gauges has puckered up and caused a serious restriction on the yellow line going into the manifold. I do not know if this o ring was like this when I tried these repairs so Im thinking maybe I didnt get a good vacuum on the system?
Today I went outside to see if I could diagnose the problem more. Static psi was 129. I started the truck and turned on front and rear ac on max, windows down. 10 minutes in I started taking readings and they are as follows..Low side 48, High 220 with no movement at all in the needles and also never any clutch cycling. Vent temps are 62F from the front and rear vents. I always grabbed the line going from the accumulator to the compressor and thought "why is that so cold and the air from the vents is not that cold", well today I noticed that the compressor is also pretty cold. Is that normal?
I am going to the part store to pick up a factory designed orifice tube and maybe install that to see if anything changes. I do not have blend door issues or a dirty evaporator, already checked that and I also installed 3 ball valves in the heater hoses to make sure the heater core has no flow. My wife and kids are going to be spending more time in this vehicle and I would like to make it more comfortable for them. Any help would be great, THANK YOU!
Just remembered, I also used duracool oil for the system instead of pag oil. I bought into that hype. Would this make a difference?
In a nutshell, poor vacuum?
Undercharge or overcharge?
How cold is the line between the front evap and accumulator? And where is the low side port, is it on the accumulator?
I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!
Low side port is on top of the accumulator. The line going from the evaporator to the accumulator is same temp, if I am remembering correctly, as the line going from the accumulator to the compressor for the front ac.
That brings up another question, how are you guys checking the temperature of the steel lines under the hood? I bought a fluke temp gun not knowing it won't work correctly in this situation. Those lines are pretty darn cold and it's showing 82-90F when I test.
Clamp-on thermocouples. But I would not expect good performance if the low side is that high. Will the low side come down if you rev the engine? Testing should be done at 1500 rpm not idle. Also try turning off the rear unit to see if you can get colder air from the front.
If condenser is not stock make sure it is plumbed correctly, in at the top out at the bottom.
I would expect high side in the high 200's at 105 ambient.
Edited: Fri August 07, 2015 at 10:27 AM by mk378
Ok I went to work again on it today. I hooked my machine up and recovered 2 lbs 14 oz, which is very low comapred to the called for 4 lbs 4 oz. My machine will recover until it hits 10" vacuum and then gives a 3 minute timer to wait for any off gassing. It sensed off gassing 3 or 4 times so it took about 20 minutes to recover the 134. Once it passed the 3 minute check I decided to recover it again and it said it pulled another 9 oz from the system, so now we are at 3 lbs 7 oz...getting closer. After that recovery I decided to change the orifice tube back to the factory tube. The orifice that I removed had material on it that looked like hair with a little bit of aluminum mixed in. It wasnt completely plugged, maybe 60%.
I closed the system back up and then pulled a vacuum. It took about 8 minutes to pull 28" of vacuum and about 40-45 minutes to get the vacuum down to 29" (I am using a Mastercool 5cfm 2 stage vacuum pump). I ran the vacuum for 60 minutes and then thought it wasnt at 29" for very long so I ran another 20 min. I let the system set for about 30 minutes and no movement in the gauges. I then charged the system with 4 lbs 4 oz. Results are not much better than it was previously. I am now getting about 55 psi on the low and 250 psi on the high with the system stabilized, windows down and max ac on front and rear, also had a large industrial fan blowing at the condenser. I recovered about 6 ounces and the low side dropped to 42 psi and High 205 psi. Front vent temps with the rear air off were about 50 degrees, rear air on it was about 58 degrees. My fan clutch is very solid and on occasion I could hear it start to move more air so I believe its good. Should I try to make another change with a smaller orifice tube to get the low side down?
I believe the orifice tube I removed today was the same size as a factory at .062. I was reading how someone was having a similar issue and found that when he installed a .056 orifice tube it fixed his pressures nicely. I don't have the pressures he was seeing but I'm willing to give it a shot. I picked up the orifice this evening. I will report back.
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