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Low side pressure is too high

metalgod3082 on Fri June 08, 2012 9:33 PM User is offline

Year: 1999
Make: Nissan
Model: Maxima
Engine Size: 3.0L
Refrigerant Type: r134A
Ambient Temp: 90
Pressure Low: 70
Pressure High: 220
Country of Origin: United States

So my A/C Compressor was leaking from the casing so I purchased a used compressor. Installed it, evacuated, held vacuum for couple hours, charged it with 1 can and the low side got up to about 50. Put another can in and the low side got to about 70. The inside temp only gets down to about 70. Since it was a used compression I thought it was the refrigerant control valve so I took the one from the old compressor and swapped it into the newer compressor. Evacuated the system again and pulled a vacuum on it, held fine, put a can of refrigerant in and same thing, low side is at 50 and high side is about 220. Anyone have any idea what could be causing this?

buickwagon on Sat June 09, 2012 9:26 AM User is offline

The vapour pressure of R-134a at 90°F is 104psi. If your static pressure is only 70psi @ 90°F, and if your numbers are accurate, then you do not have any liquid in the system. How many ounces of refrigerant does the underhood sticker call for? How many ounces per can? Did you charge with liquid (which is denser and therefore transfers more weight before pressures equalize) or with vapour (which is safer for the compressor, but may leave more refrigerant in the can)?

I've saved hundreds on service by spending thousands on tools.

metalgod3082 on Sat June 09, 2012 9:42 AM User is offline

the 70/220 is with the compressor running . Should be like 35/220. Static pressures are around 110 for Low and high when it is 100 degrees out. Compressor clutch is engaged. I put in the proper amount of refrigerant, about 24 ounces through the low side.

mk378 on Sat June 09, 2012 12:28 PM User is offline

Sounds like your new compressor is a dud. Everything was working OK before except for the leaking, right?

metalgod3082 on Sat June 09, 2012 2:12 PM User is offline

Yeah, turns out it was the Refrigerant Control Valve in the used compressor. Swapped it out with the one in the leaking compressor but didn't think that resolved the issue as low side was still 50. I think it was just really hot in the garage last night when the low side was reading 50 psi with one can in. Checked it again this morning and it was around 40. Added the 2nd can of refrigerant in and it was around 38 low side 200 high side. Inside vent got down to 50 while car is idle, while driving got down to 44 so I'm keeping my fingers crossed and hoping it will at least work through the summer. I'm gonna try replacing the case seals on my leaking compressor just in case this compressor goes out. Thank you for the replies. This site helped me few summers ago when I knew nothing about car A/C systems

metalgod3082 on Sat June 09, 2012 8:44 PM User is offline

Ok well worked fine this morning, now it is back to just cooling to about 70 degrees. Any ideas why it would be intermittently working? Blockage?

mk378 on Sat June 09, 2012 9:21 PM User is offline

If it's a SD7V16, those are infamous for getting stuck at low or zero displacement. There was a guy here years ago trying to fix the one on his VW for a month-- new control valves, etc. Ended up literally burning up his whole leave time from the Army sweating it out in Texas.

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