So I picked up a can of refrigerant today (w/ pressure gauge) because I was thinking my system needed a little pick-me-up. I hooked on to the low side and the pressure was hovering around 50-55psi. I know that is a bit high. Who knows how accurate the gauge is though...
So, I went back to the Haynes to read what they suggested you check for low symptoms. One was touching the two pipes going to the compressor. There was definitely a noticeable change in temp between the two, so that checked out.
The second was the viewing test. It said that if while the vehicle was running the refrigerant looked foamy, then you may have low refrigerant...EXCEPT if the ambient temps are very hot (its about 80 today, within what they suggest for ambient outside temp). So this got me thinking there was a possibility it was low, because it had that white, frothy look to it.
But, it also said that "With the proper amount of refrigerant, when the a/c is turned off, the sight glass should show refrigerant that foams, and then clears." This was also my case, which contradicted above.
My a/c seems to run and work fine. It blows cold, but then again I have been in some vehicles that blow COLD. I'm wondering if I can get more out of it. I know it's bad to have low refrigerant and too high of pressures, so I don't want to risk anything. Also, I have owned the truck for 5 years, and I haven't noticed the a/c getting any warmer.
Does anyone have suggestions or is this something that a 2.7 is weak on?
I just wrapped up my A/C install in my '03 yesterday, so I have some recent experience here.
At idle, my low-side was about 50psi. At the specified 1500 RPM, it drops to about 30psi. The manual says that at 1500 RPM, 86-95F abmbient, recirculation on, the low-side pressure should be to 21.3-35.5psi.
You say that the A/C is cold, but not COLD. What are your vent temperatures and ambient temperatures?
In my case, at idle I had vent temperatures of 60F. That lines up well with my low-side pressure of 50psi (54F) which should be the temperature of the evaporator. A five degree rise through the vents is believable with recirculation off and the fan on high.
On the road, I have vent temperatures of about 40F. That also lines up well with my off-idle low side pressure of 30psi or so (35F).
These were with ambient temperatures in the upper 70s.
Since my install was from scratch, I put in two 12oz cans of R134a. This is theoretically more than the system should have in it, but since you never get everything out of the cans and there is some lost to the hoses, etc, it works out about right. The system should have 19.4-22.9oz of refrigerant inside.
In operation my sight glass shows a cloudy liquid that completely fills the window. There is no sloshing or surging of the liquid. When shut down, the cloudy liquid bubbles then goes clear. I have heard from other A/C forums that R134a and PAG oil are normally cloudy in operation, so I believe this is normal. What should or should not be visible in the sight glass is a matter of much debate in the automotive A/C world.
Despite what the top-up kits would have you believe, there is no way to charge a system based on pressures only. They can tell you if the system is really, really low, but your low -side pressures will look "normal" from about 50% charge (mine looked "normal" with one can in the system) well up into over charged. As much as I hate to admit it, the only way to be sure about how much is in there is to recover the refrigerant and charge into vacuum.
I don't doubt that in many cases topping off improves the performance of the system, but since you don't know how much you need, can't control the temperatures and airflows enough to be able to use the pressures as any kind of a guide, etc. they are much more likely to result in an over-charged and poorly performing system.
In theory, A/C work is nicely scientific and precise. In practice it is almost black magic, even for the professionals.