So I am trying to add some R-134a to my 2000 Chevy Metro (yes I know this is a Ford forum. I own a Ford too). When I first investigated the A/C the clutch on the compressor would not engage and I had 0 PSI on the low side with the compressor running and with it off. I bought some $25 R-134a from Wal-Mart and tried to add it to the low side. Shortly after I started adding refrigerant the compressor clutch engaged. However after dumping about 1/5th of an 18 oz. can in, I was still reading 0 PSI on the low side with the compressor running. However once I turned the compressor off the pressure rose to 55 PSI. At the moment the low side reads 0 PSI with the compressor on, 55 with it off, and the air is still not cool. So what am I doing wrong?

Should the pressure be at 0 PSI with the compressor running? Should I be taking my measurements with the compressor off? If I keep adding refrigerant the pressure will become dangerously high with the compressor off so what should I do?

 

You need a new set of gauges.

 

You say the system was at 0psi when you started:
-Did you fix the leak that let the original refrigerant escape?
-At 0psi, the system will be full of moisture and air. Did you replace the drier and pull a hard vacuum on the system?

If the answer to either question is NO, you might as well just open the valve on that $35 can of magic and dump it into the air. The end result will be exactly the same, $35 wasted and no working AC system.

You need to, at minimum:
-Find and repair the leak(s).
-Replace the receiver/drier
-Pull a hard vacuum on the system for at least 30 minutes.
-Charge the proper amount of refrigerant, by weight, and monitor both the High and Low side pressures with a proper manifold gauge set.

Those nifty bright colored cans only serve to remove money from your wallet and little more. They can, and usually do, increase the cost of the repair after they fail to work as expected. Caveat Emptor.

With only a small amount of refrigerant in the system, the low side pulling down to 0psi, or even into a vacuum, is normal. The directions on the can some how fail to mention that, along with a lot of other important info.

 

can't think of anything to add.

well, one thing, Stay the Flip out of walfarts!

 

When one attempts to obtain a pressure reading on the low side to determine if the system is full should they do it with the compressor on or off? Is the pressure with the compressor off irrelevant? Because currently the pressure with the compressor off says the system is completely charged.

 

It is almost impossible to get a correct charge with only w low side reading unless you REALLY know what you are doing. Even then, it's still difficult to get it better than "close enough".

 

To determine if the system is full, you need to read and consider both the high and low side pressures , along with the vent temps, with the system operating. With the system off, the high and low pressures will equalize and you will read the Static system pressure. The static pressure offers little to nothing in regard to the system charge. The static pressure will also vary widely with the underhood temperature.

Checking only the low side pressure with the system running "can" indicate when you are fully charged, but it is also possible to get a Full reading in almost any state of charge if there are other issues in the system.
There is no way to tell if the Low side reading is accurate without also reading the High side. That is one of the huge drawbacks to those "recharge" kits. You can be reading "low charge" and continue adding refrigerant while the high side is climbing to the point of a dangerous hose failure or compressor failure.
Those cheap gauges are also notoriously inaccurate to the point of being useless.
The bottom line is; You are not going to fix a dead AC system for $35, regardless of what the manufacturer of that "kit' wants you to believe.

 

Not only do vent temps play a part, but ambient temp also, as well as the type of refrigerant. I think few vehicles still use R12, but there are some still around, plus many conversions from R12, and pressures on the converted systems are different yet. Throw in factors like air and moisture in the system, and things go south fast.
As stated, a good set of gauges and knowing how to use them are all important.

If the public are bound to yield obedience to laws to which they cannot give their approbation, they are slaves to those who make such laws and enforce them.—Candidus (in the Boston Gazette, 20 January 1772)

 

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