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Old 03-31-2019, 05:41 PM   #1
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AC issue, low high side pressure

Want to get some opinions on this issue. Recently bought the car and knew the AC wasn't working. Hooked the gauges up and was 0 pressure. Gave it a charge but still isn't bowing cold. Static pressure is about 55 on both sides. Turn the engine on and turn the AC on max and the low pressure side drops to 30 but the high side only goes up to around 70ish. This sounds like a compressor issue? Being mid-engined its not that easy to visualize the compressor during all of this. Are there and other tests that I can do to get to the bottom of this. Anything electrical to test? Pressure cut off switch?

I checked around with a black light to look for leaks but none that I could see. I assume there are probably some leaks somewhere since it was at 0 or the system was evacuated at some point but there is another definitely another issue going on since the high side pressure isn't going up.

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Old 03-31-2019, 07:29 PM   #2
1997, PCA Riverside
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Location: Upland, CA
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First, I would suggest, that you pressure test the system with nitrogen to verify that it will hold pressure. Nitrogen is way cheaper than 134a. Then fix any issues/leaks. Once you get the system sealed, you need to use a vacuum pump to properly evacuate the lines. Then you should (most people don't) weigh the freon charge back in. 70 is low for the high side. But the ambient temperature plays a large part for both low and high pressures. Google a freon chart for those details. You can create all kinds of problems when you add freon to a system that hasn't been pumped down. Especially if it has been open for a while.

There is also an issue on these cars with the blend door in the blower box failing. It is covered in foam and the foam degrades over time and comes out the vents. It will cause temp issues in the cabin.
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Old 04-07-2019, 12:45 PM   #3
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For future searches if anyone wants the actual answer the system was low on refrigerant. Despite 30 being in the "normal" range after more searching is appears that sometimes the low side needs to be closer to 40 for normal operation. I did this and the high side pressure came up within normal range. No leaks. Nice cold AC.

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