b737-300 Cockpit heating problem with restricted airflow

[ICETECH]

Very hard to get sufficient heat in the cockpit. This is okey for fligths below two hours but after two hours it gets freezing cold in the cockpit. Actually and indicated on the temp indicator. Air mix valve has been replaced, 190°F switch replaced, cabin temp sensors swapped between cabin and FLT deck with no change, all tests passes in the A/C bay and the duct from the mixing manifold up to the cockpit has been traced for crushed and dislocated duct. There is the feel of restricted airflow coming from the air outlets in the cockpit and the L/H pack has been verified to have less exhaust coming out of the exhaust louvers. This is actually an old problem and when the A/C went to the last C check the flight deck was re-insulated because of same problem ( 2 years ago ) but after that the A/C operated only on very short routes. It wasn´t until few weeks ago when it started operating routes above two hours that this problem was detected again.

Any input would be greatfully appreciated.

Rgds, ICETECH

[sjap]

Maybe one of these solutions?

[sr79]

if less airflow is detected in the exhaust try swapping the turbo fan valve if that doesnt help change the the turbofan assy.

[sr79]

also this might well be a weak acm but what i recommended first please let us informed

[ICETECH]

[Monkey Wench]

Hi
I had this problem on a 737 New Gen and i found the ducting which comes from the mix manifold to the cockpit was not connected.

[savmycntry]

Ice tech, Monkey Wrench hit this one good. As you know the cockpit is supplied by a seperate duct that comes off of the left supply duct. This is a smaller diameter duct that usually breaks right in the area of the fwd cargo pit where the aft wall and left sidewall corner is. The joint is tapped and it comes loose. If it is completley disconnected you will have a freezing cockpit in flight. on the ground if you run the left pack you can her the rush of air in the aft pit area. If the break in the duct is not complete you will have to take the wall down and investigate. Good luck.