ACFT EQUIP PROB MALFUNCTION MANDATES A RETURN LAND. FLC UPSET OVER LACK OF IMMEDIATE COM CAPABILITIES WITH ZDC.

Narrative

DURING CLB ACFT HAD THE R AIR CONDITIONING PACK TRIP OFF; WE RESET IT. THEN WE HAD A L 'WING BODY OVERHEAT' INDICATION. WE TURNED OFF THE L PACK AND ISOLATED THE L SIDE OF PNEUMATIC SYS. SUBSEQUENTLY THE R PACK TRIPPED OFF AGAIN AND WE LEVELED OFF AND TRIED TO CONTACT CTR TO REQUEST A DSCNT TO 10000 FT; BUT WHEN ZDC WAS TALKING TO AN ACFT ON ANOTHER FREQ AND WOULD NOT ACKNOWLEDGE OUR CALLS. WE RESET R PACK TO MAINTAIN CABIN PRESSURE BUT IT WOULD TRIP OFF AGAIN SHORTLY. STILL UNABLE TO GET ZDC (100 MI N OF GSO) WE INITIATED A DSCNT TO 10000 FT AND SQUAWKED XPONDER IDENT. ZDC RESPONDED AND CLRED US TO 10000 FT. THE CTR CTLR SAID HE WAS WORKING 3 SEPARATE FREQS. THIS UNREGULATED (THERE ARE NO RULES ON HOW MANY FREQS AND HOW MANY ACFT A CTLR CAN WORK AT THE SAME TIME) PROC OF CTLRS WORKING MULTIPLE FREQS IS A CONSTANT SAFETY CONCERN OF PLTS NOT BEING ABLE TO TALK TO CTLRS WHEN OPS REQUIRE IT. WE CALLED DISPATCH AND COORDINATED A MAINT RETURN TO GSO UNPRESSURIZED. CABIN ALT NEVER EXCEEDED 6000 FT. OUR FLT ALT DURING CLB TOPPED AT ABOUT 18000 FT. MAINT WRITE-UPS HAD PREVIOUSLY BEEN MADE ON BOTH PACKS. WE SWITCHED AIRPLANES IN GSO AND COMPLETED TRIP TO PHL.