warm air in cabin

birddog · #1 04-25-07, 10:03 PM

Problem #1 - We are experiencing excessive warm air in the cabin in our P337. The air is coming from a vent below the controll pedistal on the co-pilots side. It may be coming from both sides but the referenced vent is the most obvious. Is this bleed air and is this normal?

Any suggestions on how to control or repair this and the cause? Thanks.
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Babes Cam

Paul Sharp · #2 04-27-07, 12:10 PM

You didn't say whether this was in warm weather or not, or up high where warm air shouldn't be coming in anywhere, but could there be a problem with the vent closing properly?

Make sure it isn't exhaust air coming in from an exhaust leak.

birddog · #3 04-27-07, 12:51 PM

Paul, thanks for the reply. This warm air is constant from on the ground to at altitude. Not hot but warm. One source of air identifyed is the outlet next to the co-pilots left knee. Is there a control for that?
With the A/C running it's not too bad, but once we get to altitude the volumn from the A/C is weak (problem # 2) and we start to get a warmed up cabin all the way through landing. In the winter months it's not an issue, but starting to become uncomfortable with the weather warming up.
The Press AIR Temp controls are on COOL the FWD PASS AUX AIR is OFF the HEATER is OFF and DEFROST controll is OFF. You may have something in that one of those valves is broken allowing air to bypass.
Thanks for the input and caution.
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Kitchen Measures

Dave Underwood · #4 05-25-07, 05:51 AM

Just curious about your warm air on co-pilot's side. How well does your defroster actually work?

What serial number and year is your P337?

I have some issues with mine that are not that different as it involves the same controls.

On a P, the reason the air is warm is it is off the turbo. Look at Figure 88. The air goes through the sonic venturi restrictor on the top of the engine and then through a valve that either sends the air through the heat exchanger for cooling or to the heater. I would look at that valve first. From the heater air then goes through the firewall and flapper valve.

From there it goes to a control valve below the pilot's right foot, Figure 90 Detail C, which directs air to the defrosters or floor vents, including the vent on the P2 side. I can't seem to get as much flow through the defroster as I would like and it would appear the valve which is controlled from the panel slider is reversed.

With the first control valve after the sonic venturi in the right position actually putting air through the heat exchanger, you should get coolish air out. It is shown as item B in figure 89A in the parts manual. Figure 89A shows the best view of all the parts.

I would suggest you have a look at that first valve and then the second one. If you have a source of clean air say from a vacum to blow through the system at the venturi, you shoud be able to sort everything out.

Hope that helps and please let me know what you find.

Regards - Dave

birddog · #5 05-25-07, 12:33 PM

Dave thanks for reviewing this.The aircraft is a 1976, P3370232P and was recondition by Riley around 1990. We have not had an oportunity to operate the defroster but we will give it a go next chance and report back. I would expect we should have a comfortable cabin at altitude in the summer months (without the A/C) but it's all the A/C can do to keep up. You have given us some great information and direction and I will let you know how it goes.Thanks.
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Ipad cases

Dave Underwood · #6 05-26-07, 10:11 AM

As a further note, I think there will always be some flow out the P2 vent as the bleed off the turbo is going to be pretty constant and has to go somewhere.

Based on another look at the diagram, it would look like you can only control the front bleed air by having it go through the heat exchanger for cooling or bypassing the heat exchanger giving you warm air or hot air flow if the gas heater is fired up.

Regards - Dave