DCarlton Posted July 16, 2021 Report Share Posted July 16, 2021 I'm trying to understand the heating and cooling system on my 67 M20F. Basically trying to get the valves working freely and correctly. The right side scoop assembly (#45 middle left) appears to have a valve on the small duct outlet that's not shown on the drawing. The duct goes to a diffuser on the firewall for radio cooling. The valve shows up on the '66 drawing. Any idea how and when that valve is supposed to be operated? It's hard to access and hard to see with the carpeted side panels in place and mine appears to be frozen. Should it be left open if I can get it working? I'd also like to remove the screws (#22 upper right) to get the valve on the inside cooling air box working but I'm guessing the nuts are going to be difficult to access with the box installed. Not a crisis but working on a few details. Appreciate any insight. Thanks. 67F CABIN COOLING .pdf Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted July 16, 2021 Report Share Posted July 16, 2021 (edited) The radio cooling valve should be closed when you are flying in the rain so you don't fill the radios with water and short them out. Its in the fine print on the POH. If you take all the ducts off the airbox, you can get to the nuts. Edited July 16, 2021 by N201MKTurbo Quote Link to comment Share on other sites More sharing options...
DCarlton Posted July 16, 2021 Author Report Share Posted July 16, 2021 (edited) Just now, N201MKTurbo said: The radio cooling valve should be closed when you are flying in the rain so you don't fill the radios with water and short them out. Its in the fine print on the POH. I'll take a look. Thanks. It certainly is hard to get too. Looks like it's a manual valve with no panel control. Now that folks have cooling fans maybe it's OK to leave it closed? But I have had cooling problems with my radio stack even with a multi port fan. Edited July 16, 2021 by DCarlton Quote Link to comment Share on other sites More sharing options...
DCarlton Posted July 18, 2021 Author Report Share Posted July 18, 2021 On 7/16/2021 at 4:44 PM, N201MKTurbo said: The radio cooling valve should be closed when you are flying in the rain so you don't fill the radios with water and short them out. Its in the fine print on the POH. If you take all the ducts off the airbox, you can get to the nuts. Managed to get it working. It's been hidden behind the carpeted side panel for a long time. Trimmed the panel around the valve. A little extra air for the center radio stack should be a good thing. Thanks. Quote Link to comment Share on other sites More sharing options...
flyingchump Posted July 18, 2021 Report Share Posted July 18, 2021 20 hours ago, DCarlton said: Managed to get it working. It's been hidden behind the carpeted side panel for a long time. Trimmed the panel around the valve. A little extra air for the center radio stack should be a good thing. Thanks. Yup. I had to do the same. I just installed an airtex wall panel kit and I cut this area just a bit for easier access. I also installed a new 2.5 scat tube on that vent. The old scat tube was so tight I couldn't access the laver for the valve. I added a few inches to the length of the 2.5 in scat and now I can get my hand up there to turn the valve. New radios and modern transponders don't necessarily need cooling. Old equipment does. I just closed mine and plan on going on a few flights to see how it goes. I was getting high CO in the cabin on the ground but none in flight. I think the radio cooling tube was letting CO in while on the ground. Time will tell. 1 Quote Link to comment Share on other sites More sharing options...
mike20papa Posted July 18, 2021 Report Share Posted July 18, 2021 Flying in Texas my cabin air flow was near "intolerable". When I looked up under the panel and discovered the condition of the scat tubing - it was apparent why. When replaced it dramatically improved. Did the same for the overhead. If radios need cooling, most mfg.s now require constant forced air via a fan. 1 Quote Link to comment Share on other sites More sharing options...
DCarlton Posted July 19, 2021 Author Report Share Posted July 19, 2021 59 minutes ago, mike20papa said: Flying in Texas my cabin air flow was near "intolerable". When I looked up under the panel and discovered the condition of the scat tubing - it was apparent why. When replaced it dramatically improved. Did the same for the overhead. If radios need cooling, most mfg.s now require constant forced air via a fan. My ducting is in good condition but I don't think my heater box valve is closing completely. So there's always some heat coming in if the inside louver are open. Gotta get that fixed next. First step was to get the inside cabin air box valve cleaned up and working. Quote Link to comment Share on other sites More sharing options...
carusoam Posted July 19, 2021 Report Share Posted July 19, 2021 DC, The radio cooling isn’t cabin cooling… Delivering water to the radios kind of went out of style a few days after your vent was connected in the 60s… Check to see if the air distribution ‘panel’ is still in place… most likely, the plastic bits are still back there, not doing very much… Most panels are using some form of avionics cooling fan… and small hoses pointing at various boxes… Adjusting the valve for airflow probably got turned off one winter… Consult with your avionics guy for best air cooling strategies for your radios… PP thoughts only, not an avionics tech… +1 on clean/lubing the airflow valves that provide air to the cabin… this is at least an annual event… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
DCarlton Posted July 21, 2021 Author Report Share Posted July 21, 2021 (edited) On 7/18/2021 at 6:02 PM, carusoam said: DC, The radio cooling isn’t cabin cooling… Delivering water to the radios kind of went out of style a few days after your vent was connected in the 60s… Check to see if the air distribution ‘panel’ is still in place… most likely, the plastic bits are still back there, not doing very much… Most panels are using some form of avionics cooling fan… and small hoses pointing at various boxes… Adjusting the valve for airflow probably got turned off one winter… Consult with your avionics guy for best air cooling strategies for your radios… PP thoughts only, not an avionics tech… +1 on clean/lubing the airflow valves that provide air to the cabin… this is at least an annual event… Best regards, -a- Well yes and no. Originally both radio cooling and cabin air cooling (ventilation) originated from the left and right air scoops (plus the upper vent system). On the '67, the right air scoop has two outlets; one larger oval outlet that feeds the 2.5" round inlet to the cabin air box (cool ventilation or heat if heat is mixed from the engine bay muff). Cool air is regulated with a gate valve. There is also a smaller duct coming from the right air scoop that's controlled by a rather hidden valve with a lever; that smaller duct feeds a diffuser (or "grill") mounted on the center of the fire wall for radio cooling (per the original manuals). So radio cooling and lower cabin cooling do come from the same source. As you might expect, I've added a multi port cooling fan with ducts going directly to the modern radio trays. I was just trying to get all the original equipment working including the small valve on the right air scoop that feeds the diffuser (grill) on the firewall behind the radios. My Operating Manual states "the tube supplying the grill has a control valve near the scoop to decrease air flow in extremely cold weather". I'll probably just leave it open to get a little more air behind the radios in addition to the forced air from the newer cooling fans. It doesn't say anything about potential water intrusion if flown in the rain. Flying in the heat has prompted me to get all the air sources working. Will get more diligent about lubricating the airflow valves as recommended. Thanks. Edited July 21, 2021 by DCarlton 1 Quote Link to comment Share on other sites More sharing options...
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