The 70 PPM C/C packs installed on the B/E/Super E aircraft are notoriously fickle and usually don’t work worth a damn… The problem may or can be one or a multitude of separate problems. I recommend you try the following:
NORMAL CHECKS
1. As stated by kersey9502; check the heat exchanger for leakage using the H/E Leak Check Fitting (in the pre-politically correct USAF referred to as the “donkey-dickâ€).
2. Verify the C/C FCV is opening as required:
a. If my Can’t Remember S#*T (CRS) isn’t too bad today; I believe with GTC/Air Cart the FCV should be almost fully open.
b. Again, if my CRS isn’t too bad today; during an Engine Run the FCV should modulate to maintain 70 PPM and the position indicator on the side of the FCV should indicate about one-third to one-half open. The valve operation is affected by ambient conditions and bleed air system pressure; therefore the exact position may vary somewhat, depending on operating conditions.
c. Also, check the FCV filter and all sensing line connections.
3. Pressurize the aircraft and ensure the C/C pack has no leakage while under pressure (even though you stated “we usually fly the B airplanes from FL100 to FL140†there still is a pressure difference affect on the C/C pack and on occasion leaks will show up under pressure that do not when unpressurized):
a. Ensure the AUX Vent Valve and UFH SOV are completely closed with no by-pass or seal leakage.
4. Remove the Turbine Ice Screen and ensure it’s not damaged or clogged.
“OUT OF THE BOX†CHECKS
1. Remove the Turbine and check the shaft for fwd to aft endplay. If any endplay is present it will cause the Turbine to “slow-down†by creating excessive friction between the shaft and bearings. This “slow-down†usually occurs before the Turbine can reach its optimal effective RPM and causes low flow and higher output temperature. If endplay is present; replace the Turbine (even if new or overhauled) as I’ve seen endplay cause the problem you’re experiencing numerous times, especially in hot environments such as SEA.
2. Check the Pant Leg Duct Flapper Valve to ensure it opens smoothly and fully. The easiest way to check it is to:
a. Drill a small hole in the Duct in the upper wing root area large enough to insert a long welding rod. Insert the welding rod and repeatedly move the Flapper valve through its full range of motion ensuring it opens fully and smoothly. If it’s okay, just seal the hole with fiberglass or epoxy. If it’s not okay, oops out comes the Pant Leg Duct…
Sorry if I was a little longwinded and hope this helps, though unfortunately low airflow and insufficient cool temperatures are the nature of the beast when dealing with the older 70 PPM C/C packs, especially in hot environments.
Regards