Another Heating Question

[RacerX1166]

So, I'm a week and a half into ownership of my first 911 and loving it. I picked up the 89 Baltic blue coupe that Tim Holt had. Pics are over in the market forum.

I've got an issue with erratic airflow coming from the footwell blowers that I need some help with please. Based upon some searching, I think I know what may be going on but need help with the cause and how to address.

What's happening is that, with no rhyme or reason, when I have one or both footwell blowers on, the airflow will go from a nice consistent amount to blowing to where I thought I was driving through a windstorm. The airflow kicks up considerably and results in a pretty warm cabin. Then, for no good reason, it'll calm down. This has been happening since I bought the car but it was only today that I started to understand what was what.

I have the following circumstances (some of which may be impertinent but I like to be thorough):
- The PPI found that fuses for both footwell blowers were fried so they were replaced
- Both work now and seem to be affected as they should by the rotary switch in the center console
- The rotary switch resonates/vibrates noisily while driving
- The additional airflow seems to be random in that the boost can happen at any time; stopped, under acceleration, under braking, etc.
- the car does not have automatic climate control

I found out, during my search, that there is a blower in the engine compartment and, considering that I can make the footwell fans change speed with the rotary switch, I'm guessing that the rear fan is the culprit.

So, all of that being said, I'm asking the experts I've learned to trust and appreciate for some guidance on what I need to do to diagnose and treat this issue.

Thanks!

[Zeke]

Your car has some kind of climate control that I've yet to understand. I have it too. Since I don't really care all that much, I've never looked into it. The PO on my car said the console knobs in front of the shifter were not working. I bought a used console thinking I had to fix all problems. Well, it sits on a shelf somewhere. You might try to find out about that thing.

[imcarthur]

Edit: Ignor what I just typed. I finally read your post . . . and you don't have auto heat . . .

Ian

Here's some info but it's mainly autoheat Autoheat

[RacerX1166]

Well, I just did another recon into the car and I think it's the rotary switch. It turns out that moving from position 0 to position 1 does nothing unless I jiggle the switch. In fact, the fan will jump speeds when moving from 0 to 1 but, when it hits 1, goes back where it was.

Looks like it's the switch, which would explain the blown fuses.

So, how do I replace the switch now?

[Zeke]

Ian, great site! But, it doesn't explainn the function of the "automatic heat sensor." I was sort of inferring that something like that device might be on the fritz.

Racer, good find! I think the switch is easily accessed by removing the housing.

[vintage guy]

Sounds to me like one or more of your blowers is intermittent. Try operating the system with the key on and the engine off. You can feel the vibration on the cover over each of the footwell blowers to check that they are working and you can hear the rear blower working from outside the car. With the automatic system, the footwell blowers do not operate unless the rear blower is working. Not sure that is true for the manual system. Not sure why the rotary blower control should be making noise though. I suggest getting the Bentley service manual. Good luck.

[aj88cab]

Originally Posted by RacerX1166

It turns out that moving from position 0 to position 1 does nothing unless I jiggle the switch. In fact, the fan will jump speeds when moving from 0 to 1 but, when it hits 1, goes back where it was.

Looks like it's the switch, which would explain the blown fuses.

So, how do I replace the switch now?

Some thoughts (in no particular order):

On the manual heat rotary switch (numbered 0-3) the 0 & 1 setting are the same speed. ("0" is not "off"). If there is a surge in speed when switching between 0 & 1 that might indicate something wrong with the switch however failure of the switch is rare I think, but I wouldn't count it out. Most folks remove the passenger seat to work on the switch console.

If the footwell blowers are working then your engine blower is working. However if the engine blower is going bad and is intermitently stopping or slowing down it will affect the operation of the footwell blowers as the engine blower must be running in order for the footwell blowers to run.

Make sure the car is OFF and feel inside the engine blower fan housing. If the fan cage can rock sideways the engine blower is on its last leg and may be failing. Take the engine blower out, remove the fan housing, and check the motor shaft bushings as this is the typical failure point for this motor.

The vibration in the switch you mention could have been a problem with the servo device in an auto-heat system (dial numbered 0-9), but you indicated yours is manual heat so that one has me stumped too. I can think of nothing in there that would vibrate on a manual heat system.

Chuck's thought on an intermittent footwell blower is where I would look also. The typical failure of these blower is for them to begin to bind or seize and draw more current until they blow the fuse (or melt wires on models without footwell fuses). Please note that the fuses should be 10A, anything more is risking damage to the wires and fire.

The footwell blower fuses are "downstream' of the rotary switch so a bad switch would not, most likely, cause the fuses to blow. The fuses blow due to a problem with the footwell blowers themselves.

Do the footwell blowers make all sorts of screeching noise sometimes when they start? Take the footwell side covers off and listen carefully to each blower with the ignition ON and engine OFF as Chuck suggested. Change the speeds and see if one or both of the blowers are binding up momentarily or making excessive noise. You can try putting a 5A fuse in both blowers and seeing if one fuse blows first "possibly" indicating a problem with that blower.

A binding fan can result in the speed fluctuations you mention. Speeds 2 & 3 (especially 3) are rather noisy and blow a lot of air even in a properly functioning system.

Good luck,
Andrew

[imcarthur]

Originally Posted by milt

Ian, great site! But, it doesn't explainn the function of the "automatic heat sensor." I was sort of inferring that something like that device might be on the fritz.

Milt

It acts like a thermo switch to turn the servo on. The servo (in the console) opens & closes the flapper & grate in the heat exchanger valve allowing more or less heat through.

This of course, is not related to the OP's system.

Ian

[RacerX1166]

Been busy the last day but finally got a chance to check everything with the motor off, which I hadn't done before.

It's definitely the rear blower motor.....when either lever is pulled, it makes a ton of noise and will stop and start.

So, noob question...does anyone have photos of where said blower motor is and how to take it apart? Since the car was PPI'd and judged okay (plus winter coming), I put buying a Bentley book on the back burner until next year.

Any help on how to proceed would be greatly appreciated. Also, where are the fuses for the footwell blowers? I think I blew the driver's side while performing my test.

[aj88cab]

The engine blower is on top of the engine, drivers side. you will have to remove the black plastic pipe, then there are 3 nuts that attach it to the bracket, and the wires plug into a connector on the top of the fan. Once out it is easy to taks apart and see what the problem is. You will probably find the motor shaft bushing completely worn thru and the fan motor will need to be replaced. It is pricey but there are options using an Dayton motor, but some folks including me have found that the footwell blowers do not work with this replacement.

Here are a couple of threads I found quickly to help you understand this system. Do a search on "footwell blower" or "grainger" and you'll have a weekends worth of reading.

Help! Does anyone understand the footwell blower circuit?

Grainger Heater Blower Motor...

As for the footwell blower fuses, they are "in-line" fuses behind the footwell side covers. If one blew you probably have a bad or failing footwell blower too.

[vintage guy]

Also, our host sells a replacement blower motor for $125. It is a direct bolt-in replacement except that the the electrical connector needs to be replaced with the original one. I did this and did not have any issues with the footwell blowers not working as can happen if you use the Grainger motor.

[RacerX1166]

Here's an update and thanks for bearing with the rookie here.

I pulled the engine compartment blower motor and it definitely seems to be fried. It doesn't want to spin at all. No wobble from the bearings but there is no doubt that is was making a huge racket when I activated it.

The fuses to the footwell blowers are blown.

I plan on replacing the blower motor first and see what happens. I may be off base but I think the overloading of the engine compartment blower was what blew the fuses. I have a hard time believing that the footwell blowers are toast as well as the engine compartment blower. Add that to the fact that I drove around for two days, using the heat, and, while erratic it worked. However, when I ran the engine blower without the engine on and it bound up, only then did the fuses blow.

The noisy console switch may be unrelated but I'll have to work down to that issue. Either way, it's coming out for a bit of rework.

I didn't see a blower on Pelican except for $400+! Any other ideas? I don't want to try the Grainger thing since I'd prefer to keep the car original. I guess I need to suck it up and yell at my PPI mechanic for not noticing that loud noise in the back of the car when he got the footwell blowers working.

[aj88cab]

It is not unusual for all these motors/fans to be bad or have problems in these 20 year old cars.

You can try to clean the internals of the engine blower motor with an electrical cleaner spray then an electrical lubricant spray (I use a couple of CRC products) then a few drops of oil on the bushing. But anything you do will be temporary if it works at all. I'm affraid you will have to bite the bullit eventually.

The footwell blowers are on a seperate circuit so the blown fuses are not really linked to the engine blower. I eventually had to replace one of my footwell blowers. What I found with mine was that the fan cage and fan housing are made of plastic and had fused together from the heat. I was able to get a thin blade between them to separate and scrape the surfaces enough. then a sheet of sand paper between while running the motor to smooth the surface (all this done with the fans out of the car). Finally the cleaner, lub spray and oil again. This was temporay also (at least for one of the FW blowers).

The engine blower and FW blowers are really supplimental fans. The engine cooling fan will still push enough air thru the heat exchangers when the car is running to heat the car even if all the fans are bad. It just takes longer. That is why you still had heat.

As a temporary measure you can unplug the engine blower so the heater levers just work the heater box flappers and you will have some heat without any of the fans working.

Unfortunately in the end you will probably be buying a couple of replacement fans to get it completely right.

[vintage guy]

The rear blower motor that I used with good results is item no. 911-624-151-02-PH shown on this page:

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_VENTht_pg1.htm#item1

Depending on how much heat you actually need, there are some options involving removing one or more blowers and backdating to a simpler earlier system.

[RacerX1166]

Well, I got a new engine compartment fan assembly from egerman parts (which arrived with the housing damaged, but that's a different story). I installed it and replaced the footwell fuses earlier in the week but was unable to drive the car until this morning. Everything worked well with the car not running as I cycled all the affected fans multiple times.

After this morning's drive, I'm happy to report that everything works as it should and I get plenty of heat that is of consistent volume and velocity. I do believe that I will need new footwell blowers at some point in the future as they do groan a bit on the rare occasion.

BTW, I forgot how much fun this car is to drive! I had it out for an hour of back road apex clipping and am still grinning. I'm so not looking forward to putting her away for the winter, especially since I've had her for less than a month. I figure I've got another week, then I leave for Germany for two weeks so I'll put her in storage right before I leave. In the meantime, I've got another week off so she'll be out every nice day between now and then.

[TheGanzman]

All this talk made me check MY heater/blower system today on my newly-acquired '88 Coupe. All works well and quietly, including the rear blower motor, except that I get NO difference in footwell blower fan speeds between 0,1,2, and 3 - any suggestions?

[RacerX1166]

Joe, based on the research I did to troubleshoot my problem, it sounds as though your footwell blower fans are not actually functioning. The air you're getting is likely just coming from the engine blower.

Start with the inline fuses behind the kick panels and work your way back. Plenty of good info here if you do a search.

[TheGanzman]

Originally Posted by RacerX1166

Joe, based on the research I did to troubleshoot my problem, it sounds as though your footwell blower fans are not actually functioning. The air you're getting is likely just coming from the engine blower.

Start with the inline fuses behind the kick panels and work your way back. Plenty of good info here if you do a search.

Thanks, Sean! After I posted, I read through about two hours' worth of "heater threads". I agree that the single speed I'm getting is just the main blower doing it's thing. I'll start at the kick panel fuses and go from there...