MD-83
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew FLC complied w / Automation / Advisory
Aircraft
During cruise at 30;000 the FLOW light illuminated and we noticed the cabin was climbing. I was Pilot Monitoring (PM) so I ran the QRH for Cabin ALT/Rapid Depressurization and then Rapid Decent. At this point the cabin hadn't reached 10;000 but was rapidly approaching it; and did reach 15;000ft. The Pilot Flying (PF) initiated the descent with ATC. After completing these procedures and descending to ATC approved 13;000 feet we began troubleshooting to determine if we could get the cabin to hold pressure or if we needed to divert. ATC communication was difficult due to poor reception.I noticed that the Right Pack Temp valve was full hot and Supply pressure near 0. I cycled the supply switch off and drove the valve to cold manually and then the switch to HP Bleed OFF. The pressure then showed 28psi. I noticed the Left Pack showed 15 psi and the valve in a normal position indicating it was operating normally.With both packs indicating operative again; the Captain climbed back to 30;000 feet. We called Dispatch. We had enough fuel to continue and the cabin was now holding so the decision was to continue. The difference in pack supply pressure on L/R gauge was puzzling. To determine why there was such a difference the captain turned off the R Pack supply switch and we noted the flow light came on again and cabin began to climb. We also noted the Pressure on both gauges dropped near 0. CA turned the supply switch back to Auto and we notice the cabin held pressure again and supply gauges showed 15psi on L and 28 psi on R. This indicated to us that even though the L Pack was showing that it was operating normally; it was in fact not supplying air. We recycled the L Pack and it remained on with around 25psi the remainder of the flight.This declared emergency and rapid depressurization and descent could have been avoided if the left pack pressure gauge had indicated accurately. A similar incident can be avoided if the gauges read accurately or if a difference if pressures cues the pilot to not trust the gauges readings. There is no way to know that the pack is Off or abnormal if the temperature valve is in a normal position and the supply pressure is indicating pressure greater than near 0.
[Report narrative contained no additional information.]
MD-83 Crew reported a loss of pressurization. Crew descended to lower altitude; ran the QRH procedures and were able to regain pressurization. Crew climbed back to altitude and were able to continue to destination.