That's a pressure release valve and it's designed to release excessive pressure.
You probably overfilled your system and it spit the R-134a back out. Also, the reason your compressor was kicking on and off is there's probably a restriction in your system and the pressure is getting too high due to the lack of circulation.
There's several possible causes, none of which I should guess at. You need to hook up a manifold gauge and compare the readings to spec. If you're familiar with this process (and troubleshooting), I suggest you buy a service manual to obtain the specs and diagnostic charts.
If not, you really shouldn't try tackling this yourself. You'll need a qualified technician. And beware, all technicians aren't experienced enough to diagnos an a/c problem. You'll only pay out big bucks and have the same problem.
To get it right the first time, shop around for a specialty shop, one who has experience on Toyotas and Lexus brands.
Wednesday, March 3rd, 2010 AT 8:56 PM