I have a 90 civic that is leaking refrigerant from the bottom of the air compressor. The compressor keeps popping this little rubber cap off of the bottom of the compressor. If I hold my finger over the hole that the little rubber plug goes in, the leak stops. When I fill the system, it pops that little cap off. I tried sealing it, but it doesnt work. Is this like a blow off valve or something that says the compressor is bad? It leaks when the motor is running or not running. It just comes out as fast as it goes in. Any advice ?

Thanks.