My AC worked great last summer (3800 motor with 3800 compressor). Unfortunately it stopped working. I am assuming refrigerant is low and want to test this by recharging at a shop to eliminate other issues (bad compressor, wiring ,etc). I realize that if I have a leak, I need to find it and fix it for a long term solution

My question is, how do I know "how much" refrigerant to add without emptying the system? There is still some pressure in there, and I just want to top it up to see if compressor etc is all working properly. Is there a specific pressure that the gauges should read when I have "enough" R 134 A in the system? The local garage I use just bought an AC machine and I am not confident about their knowledge level to add the right amount of R134 without overfilling the system.

thanks

[This message has been edited by cam-a-lot (edited 06-24-2020).]

The new recovery and recharging machines are fairly idiot-proof if the technicican isn't a a complete moron. Just make sure they put in 2.1lbs refrigerant, not the original Fiero capacity of 2.5lbs

You can check the static pressure (engine off) and see if the pressure on the low and high sides is roughly equal to the ambient temperature, so if it's 70 F out, high and low side pressures should be about 70psi. With the car on, you can compare to an R-134A Temperature/Pressure Chart. The best way to charge though is by weight, recovering and recharging.

Thanks, much appreciated! You have helped many of us with our AC questions over the years...- very nice of you!

Pete

It significantly improves the chances that the next Fiero I buy will have working air conditioning.

I had a minor leak in my 86 GT that I converted to 134. I used to have to top it off every year, after winter storage. I bought a real good sealer this time, that rejuvenates the seals, and evacuated the system last summer, refilled (with gauges) with the sealer, and 134. The system held all winter, and works fine after storage...

The procedure we use for topping off a R-134a system that may be a bit low is to attach the gauge set, start the engine and then make note of the outside temperature. Then reference the temperature vs pressure chart to see what the expected high and low normal pressures should be and add refrigerant to get the system within these ranges. As a final test we measure the duct outlet temperatures to determine if the A/C is functioning correctly.

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