Hey Guys!

I got my A/C working, but colder weather is fast approaching. So I just replaced thermostat/ got my cooling system working well, so I know that's not an issue. The heater core is attached, as you can see below.




Both hoses are pretty hot going in and out of the heater core when the car is up to operating temperature. There is no heater control valve in the engine bay from what I can see, which would mean the heater core would be (in theory) hot at all times, even if the A/C was on? As of now, all I get when I turn the HVAC control to hot, all is a short burst of warm air. Would that indicate that maybe the heater core was clogged and not flowing coolant?

Further on, when I turn the temperature control to hot, there's a hissing noise. Which I'm assuming has something to do with the heater valve missing? My vacuum vent selector is working fine.
Also, it sounds like there's an airflow restriction when I turn the flap to hot, I can hear the van working harder and the airflow decreases. I don't know if that's normal?

Here's a video demonstrating, you can hear it:

You Tube

Thanks for the help dudes!

 

So if you are missing the selector valve and the vacuum line is not capped off you will not have enough vacuum at the hvac control box to operate the actuators to open and close the right doors. I would start by getting a plug for that to cap off that vacuum leak.

Second Looking at the picture I can't figure out your hoses, you should have one going from the core to the radiator, and another one from the water pump to the core. Since you don't have a valve to turn off the flow to the core you don't need a cross over hose, but it looks like the selector was replaced with T-fittings, so the water is going to go the path of least resistance which isn't through the core.

I would also using a garden hose flush the core reverse of normal flow until it run clean, then flush it in the normal flow direction until it runs clean.

Also if the hissing is inside the car, then there is a sector switch inside the hvac control panel that is known to go bad but can be easily rebuilt.

 

^^ what he said. If your heater core was routed to be hot only, there would be no need for the extra fitting and hoses there....it would be just a direct hose in, and a direct hose out. It does appear as though that X fitting is restricting the amount of coolant going in. There is always a chance too that since there isn't a required pressure being forced into the heater core, it may have gotten blocked up and now not accepting any more coolant.

 

That's super helpful guys, thanks! I'm gonna run some water through the heater core, then try hooking up the coolant lines directly through. I will also check out the vacuum situation and get that control line blocked off wherever that is.

 

You can search these threads and find the quick fix for the hissing switch.I forgot exactly what I did as I fixed mine awhile back. I added a screw or something. Once you get enough vacuum to the switch the hissing may go away on its own.

 

Does it matter which side is "in" or "out" on the heater core?

 

Update, routed the heater core from the back of the intake, and then out to the radiator. I have heat! Still need to figure out the vacuum issue inside, but I have something now.

 

There should be a hard vacuum line that use to run to where you had the t fitting replacing the selection valve. It comes through the firewall with other hvac wires. Cap this off. And see this.
https://www.thirdgen.org/forums/interior/650307-hvac-switch-permanent-fix.html

 

That solves that! But I think I'd like a control valve on the heater hoses.

Question, could I just get a simple vacuum valve like THIS to put on the line coming off the intake? The stock one has a run off that diverts the coolant through the system when the heater is off, is that really needed?

 

this is the stock part https://www.summitracing.com/parts/a...model/firebird
I'd suggest just sticking with OEM IMO

 

I just don't want an extra hose in my engine bay for no reason, also it appears that this valve is made out of metal, rather than the stock plastic one that is notorious for breaking.

 

Prob. the vacuum selector "switch" spins to change vac. settings to a different operation ie: defrost, face, floor. It is vac. operated
and is round 2 piece with 6? vac lines hooked to it. The gasket gets old and it leaks vaccuum.
Leaking vac. can cause rough idle etc.

The temp is controlled by a cable that opens and shuts a temp door. Sometimes the potmetal adjust rod snaps.
So either no heat or cold.

There are several how to fix threads so a search is in order.

So I guess it was those snake pit hoses under hood?

 

IMO yes. The heater core and the A/c Evaporator sit close to each other. If the hot coolant constantly runs through the core it will cause the a/c air and the vent air to be hotter than normal, I would try the A/c and see if it is affected. It also could make you cabin get a tad warm if the core is constantly hot.

 

I scrounged up a couple manual water shut off valves and installed them in my 84.
Sure makes the a/c colder and no more hot feet in the summer!

FUNNY my 93 Cadillac has no auto water valve like my older Caddys.
It has a restrictor 3 way tee that limits the hot water in the heater core lines.
I gotta install one of them manual; valves to eliminate my hot feet in the summer.


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