ATA 21    Air Conditioning

1 - Turbofan keeps running after pack is switched to off. 737-300/-400/-500

2 - Busy Starling Evicted Prior to Flight. 737-ALL

3 - Turbofan drain plug electrical wires. 737-300/-400/-500

4 - PACK TRIP OFF light on at higher ambient tempertures.  737-700

5 - Cabin temp is very hot in back and very cold in front. 737-700

6 - Cockpit temp is not controllable. 737-6/7/8/900

         1 - Turbofan keeps running after pack is switched to off.   737-3/4/500

Sometimes the turbofan keeps running after the applicable packswitch is set to off and there is still bleed-pressure present in the duct. This is mostly caused by the packvalve and not the turbofan valve.  When the complaint is still there, remove the bleed-pressure and apply it back on, the valve will be closed and the turbofan will stop. So replacing the turbofanvalve will not help. It is often a stucked packvalve which is the troublemaker. It happens often after a long period of non-operation, for example a heavy maintenance visit.

         2 - Busy Starling Evicted Prior to Flight. 737-ALL

The following story about the accompanying photo was submitted by Fraser Maclean, B737 Fleet Systems Specialist, Air Canada. From Aviation Safety Maintainer issue 2/2001.

According to the story, the B737 was being positioned for departure when an alert technician observed a starling departing the ram air inlet. Upon further investigation, he located this large nest in the air-conditioning ram air inlet. The nest was composed of corn, cedar and other debris that filled half a garbage bag when removed. This material was put there in less than 36 hr. while the aircraft was parked at the Ottawa airport and would have certainly caused temperature control problems with the air-conditioning pack if the aircraft had gone flying in that condition. This happened in the spring of 2000; at the time, everyone was surprised to see the large amount of material that had been packed into the inlet in such a short period. This illustrates that vigilance pays off. Although birds’ nests are expected where extended storage is involved, they can and do infiltrate aircraft on the flight line.

        3 - Turbofan drain plug electrical wires. 737-3/4/500

When you drain the oil from a turbofan, you can see two wires coming out of the drain-hole after you removed the drainplug. These wires are there for other purposes installed by the turbofan manufacturer (bearing temperature thermocouple measurements used in the shop) and are not used when installed in the 737.  It looks very strange but no worries just put them back into the hole carefully and install the plug. There is a note about it in the AMM 21-52-61 page 301 ff. See picture below:

        4 - PACK TRIP OFF light on at higher ambient tempertures. 737-700

Type: 737-700 Discrepancy: PACK TRIP OFF light on at higher ambient tempertures
during ground operation and stays off after reset.

Possible Fix: Fan bypass check valve, part # 5848999-1
Tip: And indication of this fault would be little or no airflow from the Ram
air exhaust duct outlet. Like a classic with the pack operating, place your
hand in front of the Ram inlet, check draw on your hand and compare to the
other pack. The same is true of the exhaust.
You can put your hand up the pack exhaust and feel the check valve. Removing
the aft access panel on the Plenum/Diffuser assy, gives you great access to
the fan bypass check valve to inspect it or replace it.
Reason/explanation: On the ground the heat exchangers need the check valve
closed to create a low pressure zone that pulls air through the diffuser and
out the ram air exhaust. Then the impeller fan sends the air through the
diffuser and out the ram exhaust. The operation of this
plenum/impeller/diffuser/check valve network, performs the same function as
the turbo fan on the 300/500's
Applicable reference: AMM 21-50-00-003, 21-50-00-014, FIMM 21-52-818 task 818

Thanks to Tom S. for his input !

        5 - Cabin temp is very hot in back and very cold in front. 737-700

Fleet Type: 700
Applicable Reference:
AIPC 21-23-01-20a Item #165
Discrepancy:
CABIN TEMP IS VERY HOT IN BACK AND VERY COLD IN FRONT. SEEMS TO CHANGE AROUND ROW 13.
Possible Fix:
Install Overhead duct end cap Part# 930810BC
Tip:
Pull down the ceiling panels and look for leaks of the air from the distribution duct. You can also check the airflow along the duct and look for loss of airflow. These caps are found on both ends of the distribution ducts.
Reason/Explanation:
With the end cap missing or damaged, the air gets spilled in the front of the cabin and does not make it to the aft cabin. The problem could be the opposite in the winter time. "Hot front cabin cold aft." These caps are flimsy and exand and contract when the pack is on or off.

Thanks to Tom S. for his input !

        6 - Cockpit temp is not controllable. 737-6/7/8/900

Cockpit Temperatur is very cold, than hot and cold again. The temperatur selector has no effect and the cabin temperature controler shows no faults.
Check the airfan, located downstream of the cockpit temperature bulb.If the fan is not running, clean or replace the fan. Also check the filter in the cockpit ceiling, it might be clogged.

Thanks to Thomas H. for his input !