Fresh Air Blower

[ago85carrera]

I have searched the forums and found plenty on fresh air blower motor troubleshooting but my car's problem still throws me. I've owned the car for a couple years and the problem seems to be getting worse.

The car's an 85 with standard controls for the fresh air/defogger blower (three sliders on the dash control head and 1-2-3/Defrost mode on the switch between the seats).

I don't think the blower is at fault like so many past threads point to so I did not dive into dismantling things. Here's why:

The blower turns on when the switch between the seats is turned to 3/Defrost. No screeching bearings, no protest, no blown fuses.

The blower will not turn on when the fresh air dash slider is pushed to the right (hasn't worked since I bought the car). The fan symbol on the dash control lights up but I don't know if that is a guarantee that the fan is getting power.

In addition to the blower not working at all through the dash switch, operation through the 3/Defrost switch is now intermittent. It stays on when it turns on, but it sometimes doesn't turn on. The car is a fair-weather car so I don't use the 3/Defrost switch that much but it seems to be less predictable than ever before.

Any thoughts on where I should start looking?

Thanks.

[450knotOffice]

It sounds like you've got two separate issues going on here.

The first thing you need to know is that your fresh air blower, which is located in the trunk and actually sits right behind the dash is ONLY controlled through the dashboard heating and ventilation control unit (the three levers). The switch between the seats has no control over that fan at all. The switch between the seats controls two much smaller blowers located in each footwell of your cabin (one down by your left foot and one down by the passenger's right foot). You say you have the 1/2/3/switch which tells me you have the manual heating system (the automatic system has a 1 through 9 switch). So the first thing that needs to be done to get the footwell blowers to actually turn on is at least one of the heater knobs located between the seats needs to be pulled up a little bit. That will then allow the 1/2/3 switch to supply power to the footwell blowers and control their speed (low, medium, high). You'll also hear the main heater fan located in the engine compartment come on. That fan is not controlled by the three position switch. It's only on or off with the lever position between the seats.

Back to your footwell blowers. Your intermittent issue with those fans might simply be that you don't have one of the levers pulled up. If you do then you might have a problem with the switch between the seats or you might have a problem with the series resistor that controls the fans' speed. That resistor is located in the trunk near the fresh air blower.

As for the actual fresh air blower, if you move the upper slide control lever on the dash panel to either the I, II, or III positions, you should get the fresh air blower to come on. That one slide lever is the ONLY means of turning on or off the fresh air blower. If it doesn't turn the blower on, then you most likely have a failed blower motor. It's a very common failure. Mine was failed when I bought mine and I simply found another used one from a local used Porsche parts supplier and installed it in place of the old failed unit. Works great now.

Best of luck to you.

[450knotOffice]

Also, I see this is your first post. Welcome to the forum. Now, tradition here is that you formally introduce yourself with a separate post and include at least one picture.

Cough it up buddy!

[ago85carrera]

Originally posted by 450knotOffice
It sounds like you've got two separate issues going on here.
...
As for the actual fresh air blower, if you move the upper slide control lever on the dash panel to either the I, II, or III positions, you should get the fresh air blower to come on. That one slide lever is the ONLY means of turning on or off the fresh air blower. If it doesn't turn the blower on, then you most likely have a failed blower motor. It's a very common failure. Mine was failed when I bought mine and I simply found another used one from a local used Porsche parts supplier and installed it in place of the old failed unit. Works great now.

Best of luck to you.

Thanks for the reply. You were right about the blower motor. The brushes were in pieces.

For anyone else wishing to take this on, it takes less than an hour to pull out. If you go by the Bentleys manual as I normally do, section 850 details steps for removal of the entire fresh air blower system -- that's way more than this blower motor replacement requires. You do not need to disconnect the T-duct that attaches to the trunk floor nor is it necessary to remove the fresh air intake screen and the bolts behind it. Simply disconnect the hoses, electrical harness, and control cable from the motor/fan housing and remove the two 8mm bolts.

I hope this helps those who start out going by the book.

[Mysterytrain]

ok, so it looks like you have a handle on the primative fresh air system, but I'm not totally clear if you are home free with the heating system. What 450k said is correct..but I would like to add a bit more info. Porsche got fancy and installed a temperature sensor in the heat flapper behind the driver. That sensor prevents the fans from coming on until the set point is reached. So, on a cold car don't expect to turn the fan speed switches on and expect them to spin it will take a couple of minutes. I guess the factory didn't want you to get a chill!
Another quirk is the rear blower, it must be operational to for the footwell blowers to work, although there is a mod that allows you to remove the rear blower and have your footwells fooled into thinking its there. You should have 3 different speed settings or noise settings for the footwell blowers. Positions 1 and 2 are controlled by the resistor pack that lives in the trunk behind the glove box. High speed/defrost is controlled by an additional circuit and relay. So, its possible for speeds 1 and 2 not to work and 3 to be just fine and of course, vice versa. Some cars were wired so that the footwell blowers spun when you lifted the red levers { assuming the temp sensor was hot} even with the speed switch in the zero position. The reason being the squirel cage blocked the heated air passage way and secondly the blockage got the fans so hot from not spinning that they failed...cooked bearings, fused plastic and flames. Which brings me to one last but very important note: the factory decided to play it save and began to install 10 amp inline fuses on each of the blowers. If you find that your car does not have inline fused footwell blowers then you should install them.

[RFR]

Am I correct in assuming the fresh air blower has nothing to do with the heat??

I am referring to the 3 speed rattle machine on the dash.

[ago85carrera]

Mystery Train,

Thanks for the additional insight. Your explanation on top of 450knotOffice's does help. After tackling all of this weekend's honey-dos, I only had time to dive into the trunk to pull the central blower out so yes, I've only addressed half the problem. Heater switch/footwell blower troubleshooting is for another day.

As you suggest though, maybe there's no problem with the system at all, but rather it could be the temp sensor governing the footwell fans along with the switch. On the next cold day (which I'm glad we don't see too many of in NC) I will see if the system functions according to your explanation. I saw the hot air duct sensor in the Bentley wiring diagram but assumed that was only for the auto heat systems. That system also seems to generate plenty of forum traffic so I'm glad I'm without it.

Your mentioning the resistor and relay for setting 3 also opens new possibilities. Maybe either of those are starting to fail (or fail at different component/ambient temps) which could explain my having blower air on setting 1 and 2 but sometimes not 3.

Who would guess that there'd be so much to say about a freaking HVAC system? As they say though, they're not wrinkles, they're character lines.

Long live the 911 and its vent controls which take a lifetime to master.

[joetiii]

Not to Hijack this thread

But I too have an issue relating to the fresh air blower on my 69. The motor is out and tests good both from the motor connection and the blower motor plug. Correct me if I'm wrong, but my next step is to check the contacts on the dash mount blower slide to see if they are making contact. I was reading up in Haynes last night and didn't see anywhere that discusses how to remove this control. When I looked at eletrical schematics, I see that the power comes from the same circuit as the rear defroster which also happens not to work. Seems logical that before I rip apart the dash I should check the entire circuit for power no?

If thats OK, then how do I get acces to the sliders in the dash.

[NoLift911]

I'll hijack it back - but in a different direction...I ripped all that stuff out of my Carrera - Primative is being kind. All my stuff worked perfectly and is sitting in many boxes awaiting Hershey for the next fool.

[joetiii]

How does one access the sliding front air blower fan control so I can see if it is making contact correctly?

My blower motor works fine when I run 12v to it, but not when the slider is used.

[JeffreyNMemphis]

I went to Autozone and bought a multimeter for $20 bucks. I unplugged the connection to the fresh air blower motor and tested it. On the max setting from the dash slider, I have power. The low and medium settings, I don't have power. I ordered a new blower motor from Pelican, but unless I figure out why low and medium don't power, I am only going to have one speed (max).

[joetiii]

I got some contact cleaner and the slide works much betterm but I still don't have any power at the plug so I ordered a relay and will put that in this weekend.

[JeffreyNMemphis]

Let me know how you do with the relay... I may need one too. Do you have a picture of what it looks like?

[joetiii]

My 69 has the round type relay up under the cowel drivers side. You would have to check Haynes Manual to see where the relay is for your year.

I'll let ya know if this works on mine

[rlt77]

I have a few questions on the fresh air blower controls. I have an 88 911 cab and i think it should have 4 controls on the fresh air panel, but only has 3. The top slider will move all the way from the left to the right and air will continue to increase. My question is that the blower motor runs at high speeds at all times and never shuts off. What am i missing here? i know that it is not supposed to work that way?

RT

[aj88cab]

You should have 4 levers on the control panel. Either the PO replaced it with the wrong panel, or the fan speed control lever has broken off or is inside the control panel. The Fan Speed control lever would be the right lever of two on the top row.

You feel the air increase when you move the one top lever because the left top lever controls the amount of fresh air flow.