XJ6 & XJ12 Series I, II & III 1968-1992

What is the normal static ac system pressure

 
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Old 07-14-2019, 08:04 AM
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Default What is the normal static ac system pressure

I charged the system, did everything the way I think it is supposed to be. What is the normal static pressure for this system? Does anyone know where to find the chart?
 
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Old 07-14-2019, 09:48 AM
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Depends on lots of things... The rule of thumb I use to start with for STATIC cold system pressure is... Ambient -10. So 70F get 60 PSI static on the low side. This is just a starting point..then I run the system and add refrigerant until the high side pressures are in the 200+ PSI range, (temp dependant.) Be sure to monitor vent and condenser temps. Hi condenser temps indicate insufficient air flow. Elevated high side pressures and insufficient cooling will result.
 
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Old 07-14-2019, 10:34 AM
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Mine are at about 105psi with a warm engine and system fully charged, newly (as in this morning) changed to r134a.

Temperatures are in the mid-80s here. With the system running I am getting low side at just at 40 and high side low 200s.

System seems to be cooling OK. Just never done this work before and got nervous when the system stopped (ie I turned the car off, not it broke) and I say the static pressure heading up.

Vent temp not getting massively cold, just at 58-60 maybe. But car seems comfortable enough on a sticky hot day.
 
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Old 07-14-2019, 02:10 PM
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Old 07-14-2019, 02:39 PM
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Thank you. Perfect! Since its between 85-90 today I guess I'm as close as makes no difference.
 
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Old 07-14-2019, 03:39 PM
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On my Series 3, I monitor the vent temperature with a digital thermometer.
On my last drive a few weeks ago, the ambient temperature (7 a.m.)was approx 80 degrees with little or no humidity and my vent temp was around 39 degrees.
On my trip back home, ambient temp was around 94 degrees and my vent temp was around 55 degrees.
I am running my low side at 35-37 psi and the high side at around 250-260 psi.
Today it is about 102 degrees and this is my vent temp at idle in my driveway. I took this pic to respond to your post.
 

Last edited by sanchez; 07-14-2019 at 03:42 PM. Reason: add info
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Old 07-14-2019, 03:48 PM
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This is a quote from the AC gurus:
"The low-side should be near 30 PSI at 90 degrees Fahrenheit or less. Pressure that is too much lower or higher shows there is a problem. On a properly working system, high-side pressure will be about twice the ambient temperature, plus 50 PSI.
 
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Old 07-14-2019, 04:18 PM
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Thanks Sanchez. I think it is done right. It ran and operated normally I think. My neighbor is an HVAC (residential) guy and I got his opinion and he thought it looked good.

I haven't put new insulation over the expansion valve yet, so I expect that has some effect and interestingly I am wondering if my Condensor fan is on correctly. I don't think it kicked on during my test drive. That and It seems oddly placed if it is meant to put air across the condensor. Mine sits mostly below the condensor, only a few inches of the top of the ac shroud even encompass the condesnor rectangle. I'm going to look at my parts manual and also see if I can find a picture of where it was stock. I'm wondering whether the ac was worked on at some point and the guy put the fan on underneath rather than over the crossmember. The fan is rubbing the condensor when turned by hand. I put an independent power supply to it and it ran very well, so it works.
 
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Old 07-14-2019, 04:33 PM
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Old 07-14-2019, 04:43 PM
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I added two puller electric fans to my car. In addition to my normal clutch fan, I have one electric fan on the lower right side of my radiator for my oil and transmission cooler. The other on on the left side comes on when I turn the AC on.
 
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Old 07-14-2019, 04:53 PM
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You've got a lump. I am stock/ Don't know how I'd put extra electric fans where you did. I'd only do it for the AC and I think it is OK. I had only a short drive today and AC seemed acceptable. I didn't change the condensor to a modern one. That said I live in Massachusetts so I don't need it to be icy icy just cold enough.

When I went out the evaporator valves were getting really cold and there was condensation all over it. It was dripping condensed air/water/humidity onto the exhaust manifold like a little hiss, hiss, hiss, hiss like a drop of water hitting a hot pan. I think that means the refrigerant is cold going into the evaporator. Ordered some of that goopy expansion valve insulation tape and will put that on when it arrives.
 
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Old 07-14-2019, 06:03 PM
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So remove the grill and install a pusher fan in front of the condenser. You will be surprised at the difference. There is a flat 10 electric fan available and it comes complete with a shroud. The cooler the condenser, the better the AC will cool. You may notice that at speed the AC works well but if you are in stop and go traffic, not so much. That's where the fan will come into play.
At least that was my experience. After I added the fans, no problems. Right now in Florida, its HOT,HOT,HOT.
 
 
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