Broken A/C troubleshooting
I tightened the hose connections on the manifold gauge and the vacuum pump past finger tight and they were still leaking.even after cranking down that plastic port cover I could still hear it hiss after turning off the pump. I believe it’s just a faulty unit, also only 1.8 cfm.
‘83 Platinum N/A 944
I must be doing something extremely wrong. I purchased a 2.5 cfm pump from harbor freight this morning and I’m getting the exact same results. I only have the high side hooked up as I’m waiting for my low side fitting but the low side is fully closed so that shouldn’t be affected. Testing the pump without being attached to the ac system for about 30 seconds and then it completely lets all the vacuum out. What am I doing wrong?
‘83 Platinum N/A 944
Okay I’ve done more research and I now realize I’m supposed to shut the low side valve off before turning the vacuum pump off 
I do still have the issue of my pump only being able to pull 22 hg. How much does elevation affect these readings? I’m currently sitting 4300 feet above sea level. 30 minutes into my leak test and I’m still holding pressure at 22 hg, so I’m still confused as to why the pump can’t pull full vacuum.
I do still have the issue of my pump only being able to pull 22 hg. How much does elevation affect these readings? I’m currently sitting 4300 feet above sea level. 30 minutes into my leak test and I’m still holding pressure at 22 hg, so I’m still confused as to why the pump can’t pull full vacuum.‘83 Platinum N/A 944
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Tom
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The charts say you can get to about 25.5in-Hg at 4300 feet. So you may never get to 29, but should do better than 22. Something isn't sealed up on the gauge set fittings (or adapters) -- I'd keep hunting for what it is...
I took a closer look at my manifold gauges, and I calibrated them for my elevation level as the needle was above zero when everything was disconnected. My max vacuum I can pull now is at around 24-25 hg. Will this suffice?
‘83 Platinum N/A 944
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Tom
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If you can get to 25 at your elevation, I'd say that about as good as you can expect. Make sure the pump oil is full too -- it needs that do its best...
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Tom
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Mine does when the oil is full like that.Poorsche44 wrote: Sun Jun 22, 2025 12:18 pm Yea I made sure the oil is filled to the proper line on the pump. Is it normal for them to smoke a bit by the fill port?
Okay after an hour the system is still holding pressure! Maybe dropped 0.5 hg but that also could’ve been from it settling. Is it safe to assume all of the moisture is out of the system at this point?
‘83 Platinum N/A 944
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Tom
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Was the pump running for an hour?Poorsche44 wrote: Sun Jun 22, 2025 12:55 pm Okay after an hour the system is still holding pressure! Maybe dropped 0.5 hg but that also could’ve been from it settling. Is it safe to assume all of the moisture is out of the system at this point?