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Discussion Starter #1
Hi guys-
Last summer I put in a new heater diverter valve (fun job) and ran all new heater hoses and vacuum lines. Just fixed the lower blend door on the passenger's (right) side, so heat is no longer being dumped into the rear cabin. My question is, 'Why is the the heater core even being filled with 185 F coolant when it's 100+ degrees outside?' That doesn't make sense. I assume the heater diverter valve is vacuum actuated. Does vacuum allow the flow of coolant or restrict it (what is the default if there is no vacuum)? I'm assuming either a solenoid is not closing down this valve and allowing hot coolant into my heater core. Thanks in advance.
 

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IIRC it stuck open when you don't have vacuum on the solenoid.
 

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Discussion Starter #3
So, for whatever reason (solenoid valve, vacuum leak, etc.) I'm getting hot coolant in the heater core because of Lack of vacuum? I'll check it out. Thanks,
 

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I've heard that the valve only actuates when the temperature is set to "LO". Otherwise hot coolant always flows through the heater core. Hopefully someone else can confirm or deny this. Other Saabs, like the NG900 and 9-3, always have coolant flowing through the heater core, as does the 9-5 in most markets other than the US. A/C still works fine on those cars.
 

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The ACC will bypass the heater core under certain situations where no heat is required. This includes, but is not limited to, LO setting--e.g it can also happen when you first turn on A/C in a hot car, when it essentially goes to full cooling right away, and closes the heater valve to help. I also think I've seen the valve closed when it's significantly warmer outside than the ACC set temperature, but I have selected ECON.

As the cabin temperature approaches equilibrium, then I expect the heater core to get flow so the system can fine-tune the air temperature in the duct.

A Tech II can show you if the ACC is asking the valve to close or not. You can also test the valve's operation using the Activate function (e.g. set ACC for HI, then command diverter valve to bypass the heater core.....difference in vent temperature should be immediate and obvious).
 

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Discussion Starter #6
I hadn't really thought about it, but with a computer controlled HVAC, I guess it would have to have heat available to modulate the temperature. On the old manual control systems, the last thing you would want is more heat in the dash when it's 112 F outside. On my 9-5, you can feel how warm the dash and center console side & rear covers get from that heat. They should have at least insulated the hard lines coming down to the heater core.
 

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Discussion Starter #7
So, I can always set the ACC on LO and modulate the cooling by overriding with the fan, correct? Thanks for the help / clarification on this. You guys are great!
 

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So, I can always set the ACC on LO and modulate the cooling by overriding with the fan, correct? Thanks for the help / clarification on this. You guys are great!
Yep, that would do it. That would be like putting any other car with manual climate controls on "Max A/C" and turning the fan up or down. The ACC system is always going to mix a little heat in with the A/C if it doesn't think you want it to be like a refrigerator in the cabin, but sometimes that's exactly what's needed.
 

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While you could do the LO thing, the system should do it all automatically for you. If you've set it to the desired cabin temperature but it feels a lot warmer than that, then there's something wrong.


Do you find that the dash outlets on the dash tend to go cooler to warmer as you go from the extreme right side to the left side?


My system was recently recharged and it works fine, runs at high fan speed to get the car cooled off and then idles at two to four bars on the fan, depending on the sun load.
 

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Discussion Starter #10
No, I don't find the dash vents any hotter or colder, but you do get heat radiating from the side and rear of the center console covers. They're not really insulated. Logic tells you that having 185 F coolant in an aluminum radiator inside the car just means that the AC system has to deal with that heat load also.
 

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Discussion Starter #11
Oh, one more thing. I live in the middle of the Mojave desert. I've seen it 118 F more than once here. 100 days above 100 F is not uncommon for the summer, so we struggle with heat. The solar/radiant load on our cars at work sitting in the sun brings the inside car temps well above 130 F. As you can imagine, our dashes, seats, paint, even tires struggle to survive. :)
 

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I've heard that the valve only actuates when the temperature is set to "LO". Otherwise hot coolant always flows through the heater core. Hopefully someone else can confirm or deny this. Other Saabs, like the NG900 and 9-3, always have coolant flowing through the heater core, as does the 9-5 in most markets other than the US. A/C still works fine on those cars.
this is true,.

This valve is a totally uneeded part. I have taken them out of every 9-5 I have owned for years. I live in a very hot climate and no degradation of A/C.

Many modern cars have hot coolant in the heater core at all time. Not unique to SAAB.
 

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No, I don't find the dash vents any hotter or colder, but you do get heat radiating from the side and rear of the center console covers. They're not really insulated. Logic tells you that having 185 F coolant in an aluminum radiator inside the car just means that the AC system has to deal with that heat load also.
most cars have hot coolant in the heaterr core at all time.

I like logic. But there are also facts.

This badly designed leaking valve is a long known weak point of the 9-5. ROW cars did not have this system. Only USA. Parts are from a Cadillac Citara......THANK YOU GM!!
 

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Many European 9-5s have the “starship enterprise” valve. Not sure who came up with that name. For some reason my 2004 doesn’t, although some ‘04s and later cars do.

Doug
 

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No, I don't find the dash vents any hotter or colder, but you do get heat radiating from the side and rear of the center console covers. They're not really insulated. Logic tells you that having 185 F coolant in an aluminum radiator inside the car just means that the AC system has to deal with that heat load also.
Oh, one more thing. I live in the middle of the Mojave desert. I've seen it 118 F more than once here. 100 days above 100 F is not uncommon for the summer, so we struggle with heat. The solar/radiant load on our cars at work sitting in the sun brings the inside car temps well above 130 F. As you can imagine, our dashes, seats, paint, even tires struggle to survive. :)

Okay, I'm not sure what the problem is any more.


If the A/C system is struggling to cool the car, and the interior temperature does not drop to the set point, and the fan continues to run at max speed, I would expect that the ACC will be bypassing the heater core to help cool down.


If the car can get to the temp set point on the ACC and keep it there, without running the fan at high speeds (say no more than five or six bars), then it's not relevant whether the heater core is being bypassed or not.


All this presumes a properly working A/C system.
 

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Discussion Starter #18
It's not a problem. I'm an engineer and it seems inefficient to have a heater matrix dumping all that heat (it has to go somewhere) inside the car when the passenger is asking for cooling. Does it work? Yes. Is it efficient? No.
 

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It's not a problem. I'm an engineer and it seems inefficient to have a heater matrix dumping all that heat (it has to go somewhere) inside the car when the passenger is asking for cooling. Does it work? Yes. Is it efficient? No.

It's not going to be 'dumping' heat when the blend door is only open a little bit--it is providing a bit of heat to function as a fine-tuning control for the temperature. Of course the heater box is hot, but I could really not detect any heat from the console, kick panels, or from that useless little pocket where the ashtray would go.


Whatever unwanted heat the core puts into the cabin, it's dwarfed by the heat given off by a dashboard that's heated by the summer sun. Even the radiation given off by the dash feels like it should give you a tan, except it's IR and not UV.
 
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