New car... It's HOT in here

[cwiert]

OK... so the first thing I notice when driving my new purchase is that it's hot in there! Hot air come out of the vents no matter what . The fan doesn't seem to work anyway, but i turn it off and still nothing but hot air.
This was a common problem on the 944, but that was just broken clips that caused the problem. It looks like it may be a different animal with the 928. I read something about vacuum hoses is the culprit?
Please someone tell me that this is an easy fix.

[BReyes]

I learned that coolant shut off valve (P/N 928 574 573 03) affects the temperature in the 928 cabin. It is vacuum operated and has an internal valve that fails. This is same part used in 996 tiptronic coolant system (here is pic of the part on my 996). Good luck.

Regards,

[psychII]

If you're getting hot air all the time, it is probably the recirculation flap actuator.

The rubber diaphram will cost about $20 and will take a Saturday to replace. Several WYIT. Not hard, but aggravating.

928 S4 Service - John Pirtle

Follow the link and click on vacuum actuators...

An easy way to check recirc actuator - crank your car, leave in park idling; in the passenger footwell below the glove box is a grated panel. If you can feel and push on a door through the grate, then the actuator has failed (in the open position) allowing hot air in through the vents at all times.

Using the above link and fixing the weak spots will help your ac efficiency (assuming it works). If it doesn't, you have a lot of work ahead.

HTH

[Normy]

PsychII has it right. The bad news is that to really get your climate control working right, you probably have to pull the dashboard out of the car~

The main cause of hot air from the vents is what BReyes told you about. The heater core gets heated when there is no vacuum to a vacuum servo that allows coolant to reach the device. THIS is your first check...if you have, of course....had your AC checked out? The AC on these cars typically packs it in totally at the 20 year interval. Hello? Yes, that is about right for even the BEST cars! A new compressor and some work will typically work out to a $1200 bill, which is exactly the same as a late '90's VW Jetta or a Ford or Nissan product from about the same time period.

You bought an old car; If you want AC then be prepared to pay for it! The 928 uses a Sanden compressor, same as late-'80's and up Volkswagens. Don't let an AC shop screw you!

Good luck-

N-

[cwiert]

the A/C does not work. Well, it may, i don't know because there's not even an A/C belt on the engine. I don't care about not having A/C... I just don't want hot air coming out of the vents all the time. It would be nice just to have a vent allowing cool outside air in.
I'll try the easy test that PsychII mentioned. So, in theory, that "door" through the grate should not be able to be felt if the engine is running? Where is it supposed to be? Does it get sucked in or something?

[MPDano]

They are right on the money. I have an earlier 928 and it is the same set up, but different looking valve. Stupid valve will stay open on default. No vacuum, no close. Diaphragm bad, no close. This is the source of your heat. I went through the same thing.

[Landseer]

The heater valve fails open on these. (As MP states) Its located beneath the air filter box.
If vaccum is not attached to it, it will be open, also.

Same vaccum system affects the various damper diapragms. There are good write-ups on this. Check the 928Specialists website and look for the HVAC system description written by Wally.

AC on these cars are simple automotive AC systems. Compressors are better than most and seals are serviceable. I think the 944 compressor can be used instead, and there are a blue million of those around ( check this first).

Normy is right about the cost to have them serviced. But like anything on a 928, you can do it if you are inclined.

I need to fix three cars this spring. Am looking at a total expenditure of somewhere around $600, DIY. Will be replacing O rings, seals, driers and freon 12.

[Maleficio]

Originally Posted by MPDano

They are right on the money. I have an earlier 928 and it is the same set up, but different looking valve. Stupid valve will stay open on default. No vacuum, no close. Diaphragm bad, no close. This is the source of your heat. I went through the same thing.

Sounds like the engineers decided it would be better to have heat than no heat when the system failed.

Nothing worse than driving a car in the winter with a plugged up heater coil and no heat at all.

In the summer, just roll down your windows.

[Normy]

Originally Posted by Maleficio

Sounds like the engineers decided it would be better to have heat than no heat when the system failed.

Nothing worse than driving a car in the winter with a plugged up heater coil and no heat at all.

In the summer, just roll down your windows.

It's a German car, right? I drove my '97 Jetta GLX in Memphis in the winter of 2006-2007, and there were times when I couldn't push the lock on the trunk to remove my rollaway bag, since my fingers were frozen! The heater core exploded, and I decided to wait to replace it, since they wanted $700. It was bypassed, and my fingers FROZE! During the following summer, my AC compressor lost its front seal, and the AC failed. They want several hundred dollars to fix this. I can drive without AC, even in Memphis heat, simply by driving to the employee parking lot and then putting my uniform shirt on there. I even thought about driving to the employee lot naked, but it wouldn't be necessary and it might arouse the females who check our ID's as we enter the lot.

[trust me, you don't want to "arouse" these females; they are about as wide as they are tall~]

N!

[Maleficio]

Originally Posted by Normy

It's a German car, right? I drove my '97 Jetta GLX in Memphis in the winter of 2006-2007, and there were times when I couldn't push the lock on the trunk to remove my rollaway bag, since my fingers were frozen! The heater core exploded, and I decided to wait to replace it, since they wanted $700. It was bypassed, and my fingers FROZE! During the following summer, my AC compressor lost its front seal, and the AC failed. They want several hundred dollars to fix this. I can drive without AC, even in Memphis heat, simply by driving to the employee parking lot and then putting my uniform shirt on there. I even thought about driving to the employee lot naked, but it wouldn't be necessary and it might arouse the females who check our ID's as we enter the lot.

[trust me, you don't want to "arouse" these females; they are about as wide as they are tall~]

N!

HAHA

The more I read about these German 928's, the more they make sense to me.

I'm an electrician on F/A-18C fighter jets, and those monsters are hard to wrap one's head around. It takes time, and plenty of practice to figure out how to attack a strange gripe.

What I've learned about these jets is that the engineers were constantly focused on the lesser of two (or three) evils. Every system is designed to fail in the most safe way possible, or the most life-preserving way possible.

That's the way to approach those jets: what were the engineers trying to accomplish in this very strange way they designed this circuit, or whatever you're trying to fix.

Because of my exposure to F/A-18's, the 928 seems like a very logical car to me.

But what do I know? I don't even own one, or have even worked on one before.

I sure like riding in them, though.

[psychII]

Originally Posted by cwiert

I'll try the easy test that PsychII mentioned. So, in theory, that "door" through the grate should not be able to be felt if the engine is running? Where is it supposed to be? Does it get sucked in or something?

When the car is idling, it applies vacuum to the recirc actuator (among other things). That vacuum will close the door. When the rubber bladder is split, it will not hold vaccum allowing the door to stay open = air through the vents all the time. The outside air passing over the heater core that has hot water in it b/c of the faulty water valve = HOT air all the time.

replace the hot water valve and the recir diaphram using the link I posted. You should be comfortable even if you don't care about AC.

Also, even if you don't plan on AC, you need to go through the link and find and plug all your vacuum leaks.

[cwiert]

Originally Posted by psychII

When the car is idling, it applies vacuum to the recirc actuator (among other things). That vacuum will close the door. When the rubber bladder is split, it will not hold vaccum allowing the door to stay open = air through the vents all the time. The outside air passing over the heater core that has hot water in it b/c of the faulty water valve = HOT air all the time.

replace the hot water valve and the recir diaphram using the link I posted. You should be comfortable even if you don't care about AC.

ok, thanks. i still haven't tried that test yet, but i will tomorrow. one more question in the meantime... i seem to be having relay issues in other areas of the car...any chance this heat issue could simply be a bad relay? I see relay XVIII is for "Cooling air flap adjustment." And relay X is for "fresh air blower." If either of those were bad, could that cause my constant hot air? Or are those completely unrelated to this problem?

[MPDano]

Originally Posted by cwiert

ok, thanks. i still haven't tried that test yet, but i will tomorrow. one more question in the meantime... i seem to be having relay issues in other areas of the car...any chance this heat issue could simply be a bad relay? I see relay XVIII is for "Cooling air flap adjustment." And relay X is for "fresh air blower." If either of those were bad, could that cause my constant hot air? Or are those completely unrelated to this problem?

Sounds unrelated, but do the tests then move forward.

[dr bob]

Fan doesn't run? AC button doesn't light when you push the button?

There's a relay for the HVAC that goes south, and a fuse that protects the HVAC wiring that can fail. The relay is Called "Fresh Air Blower" in position X in the 1988 cars, and the wiring is protected by fuse 17. With no power from that fuse/relay, all the vacuum solenoids go to failed position: Heater valve open, defrost vent open, center comb flap closed, etc. The fan will still run if you put the head slider at full defrost, but that give you lots of hot air in your face.

Start with the relaty and fuse, and go from there. The relay is a standard/common Bosch 53B, so you can sub i the horn relay to test if you want.

Use care pulling any relay. For sure disconnect the battery ground before you start prying the relay housing with metal tools. I have a pair of paint can openers, the ones with the rolled flat blades on the end, from Home Depot. They can reach under the relay base, one on each side, to help get the things out without breaking the covers or pulling them off. I keep a few new spare 53B's in the car, and keep the pullers in my little tool bag.

[Xlot]

Before jumping in and replacing the recirc diaphragm, test the vacuum manifold behind the control unit.

The recirc diaphragm may well be intact and the leak may be elsewhere. Heck, it may even be just the heater valve (easily reached under the airbox - has a white vacuum line to it, and if it fails, you get hot all the time).

Go read John Pirtle's write-up on testing the vacuum system including the vacuum lines for each HVAC actuator..

928 S4 Service - John Pirtle

In both my S4's, the orange line (comb flap) had a leak, and in the '89 the heater valve had failed too - all others were fine including the recirculation valve (which is a pig to get to). A leak in any of the diaphragms will cause loss of vacuum and heat.

[cwiert]

Originally Posted by dr bob

Fan doesn't run? AC button doesn't light when you push the button?

Start with the relay and fuse, and go from there. The relay is a standard/common Bosch 53B, so you can sub i the horn relay to test if you want.

Yeah, I always disconnect the neg from the batter before pulling any relays...with or without tools. The fan does run when the controls are on full defrost....but the high low knob has no effect. The fan doesn't run on any other settings. I'll check the fuse and swap the 53B relay tomorrow... good tip... thanks. That would be sweet if it's as simple as that. keeping my fingers crossed!

[dr bob]

That fresh air blower relay, or maybe the fuse is your problem. Simple cheap easy, "relay-relay-relay" is the Jim Bailey mantra. Buy a good quality relay, avoiding the cheapo imports if you can; they work for a while but don't last.

[cwiert]

Just an update with this problem. The relay was bad for the fan. Really bad with a broken prong. I replaced that and the fan worked. Then when I started up the car, that door through the grate of the passenger footwell opened. So it is getting vacuum, so that's good. It opens about 45 degrees. I'm not sure if it should open more than that. If so... I may have a leak somewhere. I haven't driven the car long enough to see if the constant heat still exists... but hopefully now that the relay is fixed, so will my constant heat problem.

[BIMMERMIKE]

This sounds like a bad/faulty sensor string problem. Outside sensor and inside sensor string broken. Check connections(possibly corroded) at outside temp sensor located in alternator cooling tube. Remove driver side headlamp or wheel splash guard.

[MPDano]