fresh air recirc change?
07-09-2009, 12:17 PM
#1
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fresh air recirc change?
As a lot of you know, it gets hot here in Texas. The 928 Climate control system works really hard to keep up with this heat. As part of the climate control, the 928 has a fresh air/recirc system that has a vacuum diaphram that is not all that much fun to replace. Since I do not want fresh air (read: blast furnace hot air) mixing with my cooled air from the AC, is there any reason that I couldn't or shouldn't change the default of the fresh air/recirc box to recirc instead of fresh air?
If I want fresh air, I will open a window or the sunroof.
What I have done is remove the vacuum diaphram and reposition the spring to the other side of the diaphram. This makes recirc as the default and makes the actuator inoperable, BUT it will keep the doggone thing closed. It also is possible to undo this "fix" if it became necessary or warranted. (in other words, it doesn't have to be permanent if you decide you don't want it that way)
My plan is to cap the vacuum line feeding this actuator to eliminate any possibility of a leak.
Any thoughts on this before I reinstall the revised assembly?
Thanks
If I want fresh air, I will open a window or the sunroof.
What I have done is remove the vacuum diaphram and reposition the spring to the other side of the diaphram. This makes recirc as the default and makes the actuator inoperable, BUT it will keep the doggone thing closed. It also is possible to undo this "fix" if it became necessary or warranted. (in other words, it doesn't have to be permanent if you decide you don't want it that way)
My plan is to cap the vacuum line feeding this actuator to eliminate any possibility of a leak.
Any thoughts on this before I reinstall the revised assembly?
Thanks
07-09-2009, 12:58 PM
#2
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I wouldn't - you will more likely get smells & mold build up on the evap in a permanently 'closed' system. You won't be getting much fresh air in the cabin (you do consume oxygen & emit CO2 like the rest of us right...?). BTW it always leaks a bit of fresh air in so you won't suffocate...
I have found it doesn't make as big a difference to the temperature as you would think - it will reduce the humidity substantially (eventually) which may make it feel like a bigger temp change than it is. - not a problem here in AZ.
What would be better is to simply control the Recirc flap separately with a switch to make control easier when you really need it - when the cabin is cooled I'd go to fresh to keep everything sweet smelling.
I do not like Porsches recirc implementation - in recirc mode (on a GTS anyway) you always get the defrost flaps open - this reduces the airflow vs vent only fresh air. More flow to the face feels cooler - so really recirc and vent only would feel the coolest (and would also cool the air the most).
The switch would need to supply ignition/x-bus power to the solenoid for the recirc flap through a diode - then you could command recirc whenever you wanted - all the standard default Recirc's will still work (e.g. DEF mode etc).
Alan
I have found it doesn't make as big a difference to the temperature as you would think - it will reduce the humidity substantially (eventually) which may make it feel like a bigger temp change than it is. - not a problem here in AZ.
What would be better is to simply control the Recirc flap separately with a switch to make control easier when you really need it - when the cabin is cooled I'd go to fresh to keep everything sweet smelling.
I do not like Porsches recirc implementation - in recirc mode (on a GTS anyway) you always get the defrost flaps open - this reduces the airflow vs vent only fresh air. More flow to the face feels cooler - so really recirc and vent only would feel the coolest (and would also cool the air the most).
The switch would need to supply ignition/x-bus power to the solenoid for the recirc flap through a diode - then you could command recirc whenever you wanted - all the standard default Recirc's will still work (e.g. DEF mode etc).
Alan
07-09-2009, 07:34 PM
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Alan,
I don't want any lingering smells ( I know I know) but I would really like to keep this thing closed when running the AC. Would there be a way to keep the actuator functional, but have the default as closed instead of open? I'm thinking that you would have to run the lever/arm out the other end of the acuator. In essence, turn it around.
I don't want any lingering smells ( I know I know) but I would really like to keep this thing closed when running the AC. Would there be a way to keep the actuator functional, but have the default as closed instead of open? I'm thinking that you would have to run the lever/arm out the other end of the acuator. In essence, turn it around.
07-09-2009, 08:02 PM
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No don't mess with the mechanicals at all - since then you aren't just changing the default - you are changing the operating sense too (e.g. it will switch to fresh air when you select recirculate - not good)
Just do what I said. - apply an ignition feed via a diode to the solenoid (in addition to its regular feed) the actuator will be active always = recirculate always. If instead you use a switch you can control it so you can turn it off from time to time - or for the winter. This way nothing is permanently modified or need be awkward to get to - with the switch off you get exactly stock behavior & with the switch on you get permanent recirculate.
Alan
Just do what I said. - apply an ignition feed via a diode to the solenoid (in addition to its regular feed) the actuator will be active always = recirculate always. If instead you use a switch you can control it so you can turn it off from time to time - or for the winter. This way nothing is permanently modified or need be awkward to get to - with the switch off you get exactly stock behavior & with the switch on you get permanent recirculate.
Alan
05-15-2020, 03:28 AM
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No don't mess with the mechanicals at all you aren't just changing the default - you are changing the operating sense too (e.g. it will switch to fresh air when you select recirc - not good)
Just do what I said. - apply an ignition feed via a diode to the solenoid (in addition to its regular feed) the actuator will be active always = recirc always. If instead you use a switch you can control it so you can turn it off from time to time - or for the winter. This way nothing is permamently modified or need be awkward to get to - with the switch off you get exactly stock behavior & with the switch on you get permament recirc.
Alan
Just do what I said. - apply an ignition feed via a diode to the solenoid (in addition to its regular feed) the actuator will be active always = recirc always. If instead you use a switch you can control it so you can turn it off from time to time - or for the winter. This way nothing is permamently modified or need be awkward to get to - with the switch off you get exactly stock behavior & with the switch on you get permament recirc.
Alan
05-15-2020, 12:43 PM
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Just route the vac source of the actuator to a constant source of vaccum...ie. The black line that actually feeds the HVAC distribution valve block.
T the blue line into the black line. You will have to cap the port or the entry to the HVAC distribution valve where the blue line goes because when it is signaled to open you will cause a vacuum leak.
as soon as you start the car it should open rigged like this. If you also add the orange line for the center comb flap, it will stay up all the time also and help with not restricting airflow... BTDT
T the blue line into the black line. You will have to cap the port or the entry to the HVAC distribution valve where the blue line goes because when it is signaled to open you will cause a vacuum leak.
as soon as you start the car it should open rigged like this. If you also add the orange line for the center comb flap, it will stay up all the time also and help with not restricting airflow... BTDT
05-15-2020, 01:09 PM
#7
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Just route the vac source of the actuator to a constant source of vaccum...ie. The black line that actually feeds the HVAC distribution valve block. T the blue line into the black line. You will have to cap the port or the entry to the HVAC distribution valve where the blue line goes because when it is signaled to open you will cause a vacuum leak. as soon as you start the car it should open rigged like this. If you also add the orange line for the center comb flap, it will stay up all the time also and help with not restricting airflow... BTDT
@Alan indicated a method of activating the vacuum solenoid using switched voltage and a diode. I was looking for more information on this method. I understand the line voltage, but dont understand the function of the diode.
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05-15-2020, 03:30 PM
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I made different changes (rather more extensive) but it should be possible to implement this in the console at the AC head unit. For an S4+ Pin 9 on the head unit main connector is the feed to the recirculate solenoid, and pin 10 is the power in to the head unit. A switch installed between these (even without a diode) will let you switch between full time recirculate (switch closed) and normal HVAC operation (switch open).
If high summer heat is your problem also consider the hot water valve operation. On hot restarts you will have a lot of heat in the HVAC system because the heater valve always opens with the car off. Convection flow causes the heater core to fill with hot coolant and when you restart it will take a many minutes to return to full cooling as this heat dissipates. This not a problem for single long drives with enough time for the heater core to return to ~ambient temperature before you drive again, but with lots of short stops its a real pain. You can tell Porsche built the 928 with primarily cold climates like Germany in mind.
Ideally the hot water valve would stay open on shutdowns in winter temperatures and stay closed on shutdowns in summer temperatures. This too can be done - but its a bit more tricky. Many people in hot climates just zip tie the heater valve closed for summer.
Alan
If high summer heat is your problem also consider the hot water valve operation. On hot restarts you will have a lot of heat in the HVAC system because the heater valve always opens with the car off. Convection flow causes the heater core to fill with hot coolant and when you restart it will take a many minutes to return to full cooling as this heat dissipates. This not a problem for single long drives with enough time for the heater core to return to ~ambient temperature before you drive again, but with lots of short stops its a real pain. You can tell Porsche built the 928 with primarily cold climates like Germany in mind.
Ideally the hot water valve would stay open on shutdowns in winter temperatures and stay closed on shutdowns in summer temperatures. This too can be done - but its a bit more tricky. Many people in hot climates just zip tie the heater valve closed for summer.
Alan
05-15-2020, 04:32 PM
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I made different changes (rather more extensive) but it should be possible to implement this in the console at the AC head unit. For an S4+ Pin 9 on the head unit main connector is the feed to the recirculate solenoid, and pin 10 is the power in to the head unit. A switch installed between these (even without a diode) will let you switch between full time recirculate (switch closed) and normal HVAC operation (switch open).
If high summer heat is your problem also consider the hot water valve operation. On hot restarts you will have a lot of heat in the HVAC system because the heater valve always opens with the car off. Convection flow causes the heater core to fill with hot coolant and when you restart it will take a many minutes to return to full cooling as this heat dissipates. This not a problem for single long drives with enough time for the heater core to return to ~ambient temperature before you drive again, but with lots of short stops its a real pain. You can tell Porsche built the 928 with primarily cold climates like Germany in mind.
Ideally the hot water valve would stay open on shutdowns in winter temperatures and stay closed on shutdowns in summer temperatures. This too can be done - but its a bit more tricky. Many people in hot climates just zip tie the heater valve closed for summer.
Alan
If high summer heat is your problem also consider the hot water valve operation. On hot restarts you will have a lot of heat in the HVAC system because the heater valve always opens with the car off. Convection flow causes the heater core to fill with hot coolant and when you restart it will take a many minutes to return to full cooling as this heat dissipates. This not a problem for single long drives with enough time for the heater core to return to ~ambient temperature before you drive again, but with lots of short stops its a real pain. You can tell Porsche built the 928 with primarily cold climates like Germany in mind.
Ideally the hot water valve would stay open on shutdowns in winter temperatures and stay closed on shutdowns in summer temperatures. This too can be done - but its a bit more tricky. Many people in hot climates just zip tie the heater valve closed for summer.
Alan
i have 2 pieces of string attached to the arm of the valve. In the winter season i pull it to ON in one direction.....in the summer i pull it to OFF from the other side to close it. Now and then i open it to circulate water through the core.
need all the help i can get here. I rarely have that valve open
