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The a/c is finally working properly, with evap temp hovering between -0.5 and 0 deg on temp setting Lo, fan on max and engine up to 3000 rpm and the pressure reaching 180 psi. I had earlier wriggled the pressure sensor connector and wires where there must have been a contact issue. With temp set to 21 deg and middle fan speed, the evap temp rose to 7-8 deg, but began dropping again when the temp was set back to Lo.
Low side pressure of 350PSI means something is drastically wrong.
If you can con the AC guy to give it a good vac and put in the exact amount of R134a all should be good.
As long as the dryer is the same size as the original,sometimes if it isn't the measured weight can be not quite correct.
The condenser with attached dryer that is a copy of the original was fitted and since then the low side pressure has always been lower than static when the system is cooling, so that 350 psi situation is now history.
Unfortunately the good working system was short-lived. I think there is a wiring issue, possibly with the connector next to the battery in which the a/c wires from the engine harness are located. Alternatively there could be an issue with the engine fan for which I haven't yet found the actual speed in the Gap tool, only the commanded duty cycle although I haven't moitored it yet as I keep loosing my live value selections when I try to save the selection. I also have yet to connect my little scope to the compressor valve feed to confirm that the ATC is no longer sending a high duty cycle signal trying to open the valve once the system stops cooling.
Unfortunately or otherwise its too windy for me to get back to my urgently-needed weed spraying, so I'll keep at it for another hour or so.
Unfortunately the ATC module is supplying full battery voltage to the compressor control valve, excepting for regular short intervals of approimately 5% duration of 0V. This, with the observed high-side and low-side gauge pressures, means that the control valve isn't increasing the compressor capacity as required by the ATC module. The valve must be increasing capacity slightly as some pressure increase is observed along with slight cooling at the evaporator, moreso as engine revs are increased.
The ATC power to the control valve ceases whilst ever the pressure sensor connector is unplugged, but resumes immediately the connector is refitted. The ATC power to the valve is unaffected if the engine fan's connector is unplugged.
Hopefully we can arrange to have the system thoroughly flushed to clean it out without removing any components.
Edit: I'll try switching the a/c on and off at higher engine revs to see if the bursts of higher pump volume can dislodge any contamination of the valve.
My experience with VW control valves is once they're done, they're done. The valves have fine screens on the inlet side. If stuff has gone in there to jam the valve, then it's done.Quote:
Originally Posted by Graeme
These valves have a screen around the outside but the symptoms don't indicate to me that the screen is permanently almost fully blocked.
Switching the a/c on then off with revs eventually caused pressure to build, up to 210 psi around 3000 rpm but easily 180 psi 1500+ rpm. However going up and down in revs would eventually cause pressure to drop right back and evaporator temperature rise indicating that the valve was no longer being opened, but it was quite easy to get pressure again. I'll have another stint later to see if I can clear whatever is causing the pressure fault.