964_944

So it appears that my rear blower (on the engine) has gone the way of the dodo, but how can I verify that it isn't another component before I shell out money for a replacement? Symptoms are as follows. Setting the temperature above anything but the lowest setting and I don't hear the fans turning on in the dash. Could it just be the temp sensor? Even when warmed up, the car will not blow/pull heat into the cabin.

The only warm air that is getting past a bad servo for the passenger footwell is getting by at this point. That is actually enough to keep me plenty warm, but it nearly melted my wifes shoes the other day so I know I've got to replace that as well. Is my no dash fan with heat on problem related to the bad servo? To the fan in the engine compartment?

Any ideas are greatly appreciated. The temperature is dropping, but I'd still like to drive the car if the roads are clear.

Thanks!

Computamedic

You need to confirm if the rear blower is running. With the heat selector off blue the rear blower should start up. You can hear it fairly easily without the engine running. If it doesn't start up the dash blowers will not run. Most common causes of the rear blower failing to run are a blown (30amp) fuse or a failed relay. You can use the oil cooler or a/c relays from the front electrical panel to check since they are the same type of relay.

If you are getting warm/hot air into the passenger footwell it sounds like your rear blower may be working anyway since it's unlikely it would get there without it's help.

Hope that helps.

Regards

Dave

964_944

I'll try that first, but I don't think it's running. I used to be able to hear it and now I don't. I do hear fans in the front when I put the heat selector on "blue", but if I go up more than two clicks, they turn off. From what you are saying the fronts shouldn't run at all if the back one isn't working, correct?

Computamedic

The dash fans will stop quite quickly if heat is selected (i.e. off the blue dot) and the rear blower doesn't run. What you describe is exactly what happens with no rear blower.

Dave

964_944

Perfect. That's what I wanted to confirm. I've checked all the fuses and they seem to be in order, so I'll test the relay as you have described next. If it's not the relay, then I'm sure the fan is kaput. Thanks for the assistance so far!

evoderby

The symptoms indeed indicate a non functioning rear blower. To check whether the blower itself is at fault is easy enough, just disconnect the electrical plug and hook up a 12V feed from a spare battery (a small battery from a 12V cordless drill comes in handy for this).

If the blower is not running after hooking up this direct feed, it takes about 5 minutes to remove the complete unit to further investigate the cause. Could be as simple as a poor connection of one of the feed wires or more serious problems with the motor itself.

At this point you have to decide between having the motor refurbed, buying a new one at about € 450 or delete the blower altogether through using a Cup/RS heater duct. The latter requires shorting the rear blower relay as described on RL in order for the heating to function correctly.

I have the RS duct installed, which tidies up the engine bay with better access and about 2kg weight saving as an additional bonus. We curently have snow where I live (Amsterdam) and the heating works fine...

Rgds,

Harald

Crystal Cranks

You may want to check the connection for the wires INSIDE the fan as they have been known to come loose, just remove the cover to check.

911porschefan

Harald

Do you have a link to shorting out the relay? I have the same problem, I know I need a rear blower motor, but don't want to replace it yet. I want to see how much heat I get from it without the motor. I live in Canada and sometimes it reached -20C where I live, I wonder if without the motor I will get enough heat.

Millemiglia

I've been planning to do this myself but I even after looking in PET I think it's a bit unclear how to do this...
Is there three bolts to undo?
Seems a bit difficult to reach with the engine in....

evoderby

https://rennlist.com/forums/6389608-post18.html

Please be aware that at higher engine revs the bulk of the heating system air flow comes from the belt driven engine fan, not the electric rear blower. Early 911's didn't even have a rear blower.

When keeping a non functioning blower in place however, my guess is it will act as a substantial restriction....