Can I safely jumper between either G or Y and RC at thermostat panel to troubleshoot AC problem?
The short answer is "Yes you can", but I would hesitate giving a DIY this information without knowing how much experience he has in controls and troubleshooting. True a thermostat is simply a set of switches but you are also bypassing many protective devices used to stop a sequence to protect your equipment. This type of procedure in my circles is infamously known as a "smoke test" or a test of last resort. So if you decided to do it. Be prepared to replace other parts you may damage.

Good luck.