AC Charging / Diagnostics

[crbeasley01]

Hi All,

I have a 1999 VXR that I've had throughout the Middle East and am now in North America. Fairy recently the AC compressor was replaced, and the system was charged somewhat recently too. None the less, there must be a small leak and the system is empty again. I went to go charge it and got myself a set of manifold gauges and couple R134 cans. After running the vacuum gauge for about an hour on it, I go to charge the system. I hook the can on, screw in the pin on the top of the connector that goes on the can, and open the low pressure side with the car running, cool box, rear, and main AC all on max. The gauge jumps to about 55 psi but the compressor never cuts on. Wondering if its the compressor, the low pressure sensor not letting it cut on (and if so perhaps because I am filling wrong?). I am leaning towards the pressure not actually jumping up in the car. When I tried bleeding the yellow line I'd here a little preasure release, and then stop, but no real spray coming out. Also I should be observing more in the window I would assume?

Thoughts? Probably a pretty rookie question but reading through the other AC help threads and youtube videos I am stumped as to what I have wrong.

Thanks all!

 

[jsloden]

Before I start the car and try to fill from the low side I normally charge the high side first WITHOUT THE CAR RUNNING. Let some pressure build up in the high side, shut the valve off, start the car, then charge the low side. This keeps you from possibly having to jump the low pressure switch to make the compressor come on. It also saves time charging overall.

 

[styran]

I have my EPA cert. I always charge cars via liquid down high side with engine off. cut yellow line off at manifold when weight is correct, close of high side connector, and start the engine to pull the refrigerant in the red line into the suction side. AC work is not the easiest to DIY. if you are uncomfortable or do not understand, do more research or take it to somoene who knows how to do it. you dont need ten thousand dollar machines to work on cars AC. anyone who tells you that is full of s***

 

[crbeasley01]

Tried a couple things.

I thought maybe my r134 can was out so swapped to a new one. The old one seemed to have some liquid but no charge. Using the new can brought the low pressure up higher from about 50 to 70psi.

As suggested, I tried with the engine off preloading the high side, it took some pressure but not all the way to the factory recommended pressure for full.

I tried then to jump my MGC relay to check that my compressor was working. It started spinning. With it on, I reopened the low side and expected the pressure to drop here and high to increase but again nothing. Just stays here.

 

[styran]

Tried a couple things.

I thought maybe my r134 can was out so swapped to a new one. The old one seemed to have some liquid but no charge. Using the new can brought the low pressure up higher from about 50 to 70psi.

As suggested, I tried with the engine off preloading the high side, it took some pressure but not all the way to the factory recommended pressure for full.

I tried then to jump my MGC relay to check that my compressor was working. It started spinning. With it on, I reopened the low side and expected the pressure to drop here and high to increase but again nothing. Just stays here.

View attachment 4122857

Cars AC systems are charged by WEIGHT, NOT PRESSURE. the AC system has a pressure switch on the liquid line to prevent the compressor from activating with low line pressure. low line pressure = low refrigerant flow = low refrigerant oil flow. operating the AC in this scenario will damage the compressor, causing it to send metal particles throughout the AC system requiring expensive repairs. On my LC the switch allows the compressor to activate around 28 PSI. i would start by making sure this switch is working. Tom Lech is a good resources on car AC. Toyota also has an evaporator temperature sensor which will shut off the compressor if the temperature is too low (to prevent evaporator freezing up). From ambient pressure, suction pressure should drop when compressor is running, discharge pressure should rise. once everything stabilizes you will not see much change in the gauges

 

[crbeasley01]

Aw figured it out. As I expected, PEBKAC as they say in the tech world (aka. I'm an idiot). The valve is righty loosey lefty tighty on the low pressure side? As soon as I opened it up the other direction things got flowing. Not sure why I watched the youtube video, wondered why he did it that way, and just assumed it was an odd video rather than the proper method... Time to load it up with some dye and see what is going on