Hey Guys, Maybe this is simple, I've never actually got my mind around how the whole heating/cooling system works.

When driving, i get pretty good heat through the vents and defrost. But when i stop, it starts blowing cold. Basicly, if the RPM is low, it blows cool air, but if i step on the gas it'll blow warm again.

I'm thinking that it might be that plastic valve looking thing located on the passenger side of the engine, looks like it routes the hot coolant into the firewall. Not sure how it works, so i don't want to start replacing stuff without knowing a little more then i do.

It's really starting to get annoying now that i got a remote start, and it's getting cold. No point if the darn car is still freezing. lol.

Ohh, FYI it's a stock 305 TBI (5 speed if it matters)

Thanks for any help guys (and gals)

Here, i highlighted the 'valve' i'm talking about.

Shoot, if you can tell me what it's called i'll be happy. lol

Heater comtrol valve, cost around $50 at Auto Parts store.

50 bucks? ...aka, hit the junk yard. lol.

Thanks.

are you sure your radiator is full? That sounds more like a low coolant level problem than a bad control valve..
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on a side note that pic u posted, is that in a junkyard or something? Or sitting outside without a hood on it?

its called " heater diverter valve " . i changed mine a month or so ago . around $20.00 at advance . check all hoses & vacuum lines . when i put a system press. tester on my radiator it was leaking from the top of the valve .
i also relocated mine to the rt. rear corner of eng. bay , no special hoses req. . sure cleaned up eng. bay . do a search on heater diverter valve , it will tell you how to .

mine was doing that and i just had low coolant.

Sounds like low coolant to me as well. If not that, low vacuum.

... i need to wake up... lol. i never thought about checking the coolant.

If that fixes it, I'm going to feel like a big A-hole. lol. I dunno, just automatically started thinking something more complicated.

*shakes head*

K.I.S.S.

You can delete it for like $2

Only drawback is coolant will constantly flow thru your heater core

What does the valve do? It was too bulky, and i just removed it, figured my old carbed car never had one, how important could it be?

Valve helps the car warm up faster by not circulating coolant through heater core. Emissions thing. Most vehicles don't have them.

Also I know without this Valve your heating and cooling will not work.

Actually it has nothing to do with that. The reason it is there is because the AC heater box blows cold air over the heater core when the AC is on, so if you had a hot heater core it would warm the cooled air

actually I think the air always goes over the ac and only goes over the heater core when you want heat, this is so it can pull the mosture out of the air when you have it on defrost. if it always flowed over both there would be no way of controlling temp.

Hence the reason the coolant diverter valve is there.......

We have found in upstate NY that numerous people have heating issues with their cars. Usually it a thermostat, or low coolant. After they change everything we tell them if you still don't get heat, you might want to flush your block and cores out. I have heard this can be done with Draino if you know what your are doing. Never run it in your engine though. Remove your heater core lines and pour it in a line directly. Does do a nice job or removing all the gunk built up.. Then flush completely before hooking up .

Yea, i wasn't totally out of coolant, but it was low-ish. So, i'll see this afternoon if it helped.

Correct, the amount of air that is allowed over the heater core is controlled by the blend air door inside the air ducts. If you move the lever all the way over to cold the air door blocks off the heater core, all the way to hot and the door is wide open, and anywhere in between depending on where you have the lever on the control head. The dirverter valve simply stops coolant flow to the heater core on the Max A/C setting, if you remove it your heat and air will still work, it may be a few degree's warmer with the a/c on though.
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let us know how you make out, also have you figured out where the coolant went? It had to go somewhere.. Have you done a pressure check?

The diverter valves function is to shut off coolant flow to the heater core on the Max A/C setting. Not all third gens were equiped with one from the factory.

Yea, actually i did see where the leak is. It's leaking slowly at the fixture, directly under the over-flow port. I believe thats the hookup for the coolant diverter valve. I think it just need tightend

If you want to make sure there are no leaks you can borrow a cooling system pressure tester from autozone if you don't have one. That way you can pressure test the whole system and the cap.

Ok well i removed my AC, im only interested in heating in summer nights while at the track. Foggy windshield is not fun at 95 mph....

Thanks for the info.

Yes pressurizing the system is a good idea.. Autozone has a loan a tool program that will let you rent just about any tool and return your money once they get the tool back as long as it isn't broke.