With the low (blue side) and the high (red side) hoses now attached to their
respective ports on the TJ, I opened the valves on the service port couplers.
The valves there are used to "trap" the refrigerant in the hoses so that when
you remove the hoses from the system, you do not release refrigerant into the
environment. When I opened these valves, it actually connected the hoses
to the a/c lines in the Jeep.
Next, I opened the two valves on the gauge manifold. With these now open, I could read the static pressure (compressor is not running) on the a/c system. It was sitting at approximately 120 PSI.
The on the ambient air temperature affects the pressures you will read when running the compressor. The tables in the factory service manual span a range of air temps in 10 degree steps. We turned on the digital thermometer that Alan uses and found our ambient temp was just a bit over 90 degrees. Close enough....the 90 degree column in the pressure table would suit our needs just fine.
According to the manual, I would be expecting a low pressure of 38 to 47 PSI and a high pressure of 250 to 300 PSI if the system was charged with the proper amount of refrigerant. The center vent temperature should be in the 37 to 48 degree F. range.
It was time to start the engine, set the A/C to recirculate, and put the blower fan to high the setting. After several minutes of operation, I checked the pressure gauges. As shown above, the low pressure gauge was 30 PSI and the high pressure gauge was about 205 PSI. The center vent temperature was about 57 degrees.
As we suspected, the system appeared to be a little low on refrigerant. It wouldn't take too much to bring the numbers up into the proper ranges by adding a little refrigerant.
With the engine and compressor still running, Alan opened the valve at the top of the R-134a container. I saw an immediate jump on the low pressure gauge. Alan said this is normal as we are now seeing can pressure on the low pressure side. Immediately, the can began to get cold....a sure sign that refrigerant was being transfered from the can into the low pressure line.
To speed the process along, I set the hand throttle to about 1400 RPM. After another 30 seconds or so, Alan closed the valve on the R-134a container so I could get an accurate reading on the gauges. We were better on the numbers but still a bit below what the manual said we should get, so the valve was opened again to add a bit more refrigerant.
I was keeping an eye on the digital thermometer that we had pushed into the center vent. It was slowly dropping as we added refrigerant. When it hit the 45 degree point, Alan closed the valve on the R-134a can and I took another look at the gauges. That was better.....low pressure was hitting about 41 PSI and the high pressure reading was a bit over 250 PSI. We agreed that it was pretty good and I was happy with the numbers we were seeing. Yeah, we probably could have added another ounce of refrigerant, but 45 degree air was OK with me.
The valves on the gauges and couplers were closed (trapping the R-134a refrigerant in the hoses) and I removed them from the A/C service ports. Alan shook the R-134a container and estimated that there was an ounce or so left which meant we added about 3 ounces to the system.
That 3 ounces probably doesn't seem like much, but as you can see, it was enough to bring the system into spec and drop the temp by 10 degrees. An important point here....it would be VERY easy to overfill the system with just a 12 oz. can of refrigerant if it were in the same situation as mine....a little low but still making cool air. Alan said that the old R-12 systems were more forgiving and could tolerate being over filled more than the R-134a systems. I am glad he had the gauges available as it provided us with an accurate method by which to accomplish this maintenance work.
Unless something down the road indicates otherwise, I should be
good for a few more years (with any luck) before I need to do this again.
Of course, anything can fail and if it does, I guess I'll be doing something
else to fix the problem.
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