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Found this shut off valve on the return hose from the heater core.

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Found this shut off valve on the return hose from the heater core.

Old 09-09-2018, 03:11 AM
  #1  
Haggisbash
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Default Found this shut off valve on the return hose from the heater core.

I haven't got a FSM yet but I figure this is not a standard item on a '93 LT1.
Wondered why the air con would only blow cold on this new to me car. Question is why would someone fit this? I'm having thoughts that there is some sort of problem with the blend door and this was a way around having to fix it?


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Old 09-09-2018, 06:18 AM
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It almost looks like one of those Prestone hose flushing adapters.
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Old 09-09-2018, 07:40 AM
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Pretty sure that is what that is. If you don't have heat I would suggest you check the blend door actuator. The connector that attaches the arm to the blend door under the dash is notorious for breaking. On my 88 it was the opposite problem though. Heat was on while I was running AC.
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Old 09-09-2018, 08:32 AM
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I agree with whaleman and cdm747 - that looks like a flushing "T" to me too. Unscrew the cap, and see if it looks like a plastic "T" fitting. (the cap will probably have the same thread as a Garden hose). Those flushing "T"'s do have a propensity to leak after a while - so make sure the hose clamps are good and snug, and the washer under the cap is in good shape.
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Old 09-10-2018, 01:50 AM
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I took the cap off when the engine was cold and it is indeed a flushing T. So with further testing I have found that the two heater hoses are getting warm but no heat in the cabin, seems the most likely cause is the blend door not working. I'm annoyed with myself because when the car was inspected before I bought it testing was done to make sure that the air con was blowing cold but not hot
Can anyone point me to a "how to" for testing/inspecting the blend door? Preferably starting with the blend door is located........ I have no idea where it is
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Old 09-10-2018, 07:43 AM
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Originally Posted by Haggisbash View Post
I took the cap off when the engine was cold and it is indeed a flushing T. So with further testing I have found that the two heater hoses are getting warm but no heat in the cabin, seems the most likely cause is the blend door not working. I'm annoyed with myself because when the car was inspected before I bought it testing was done to make sure that the air con was blowing cold but not hot
Can anyone point me to a "how to" for testing/inspecting the blend door? Preferably starting with the blend door is located........ I have no idea where it is

Remove the blower motor module/resistor assembly. It is right on top of the heater case. You can look right down in the hole with a flashlight and see the blend door.
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Old 09-10-2018, 07:46 AM
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Easiest thing to me would be remove the blower control module located on top of the blower housing. Look down and towards the fire wall through the hole the module comes out of. Have someone change the setting from AC to heat and you should see the door move. It is simply a door that separates the heater core section from the housing. If that door doesn't move you probably have a broken connector on the actuator rod and will have to fix it under the dash from the inside.
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Old 09-10-2018, 10:39 AM
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Not having hot air shouldn't be a deal breaker if the rest of the car is in good shape. It is a minor problem and not to difficult to fix. A 25 year old car will have some issues.
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Old 09-10-2018, 07:11 PM
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Originally Posted by 383vett View Post
Not having hot air shouldn't be a deal breaker if the rest of the car is in good shape. It is a minor problem and not to difficult to fix. A 25 year old car will have some issues.
LOL yeah I'm used to issues, I've also got a '70 C3 that has thrown all sorts of issues at me since I bought it in 2012. Ironically keeping heat out of the cabin has been a challenge on the C3!

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Old 09-11-2018, 01:10 AM
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Tested blend door and it is working fine, so no further ahead on why the heater doesn't heat the car
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Old 09-11-2018, 06:57 AM
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Get the engine up to normal operating temperature. Feel the hoses on both sides of the heater core to see if there is water circulating. Both hoses should be about the same temp.
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Old 09-11-2018, 06:59 AM
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The heater hoses should be too hot to touch. What is the engine temp going down the road?
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Old 09-12-2018, 12:51 AM
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Originally Posted by ex-x-fire View Post
The heater hoses should be too hot to touch. What is the engine temp going down the road?
Hi, engine temp sits at the first mark on the gauge, I reverse flushed the heater core and voila we have heat There didn't seem to me to be a lot of crud in it but obviously it was enough to upset things.
The car has some sort of Hypertech chip in it which I assume is something to do with the engine cooling because it seems that as soon as you start the engine one of the radiator fans comes and never seems to turn off.
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Old 09-13-2018, 03:51 AM
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Originally Posted by Haggisbash View Post
I haven't got a FSM yet but I figure this is not a standard item on a '93 LT1.
Wondered why the air con would only blow cold on this new to me car. Question is why would someone fit this? I'm having thoughts that there is some sort of problem with the blend door and this was a way around having to fix it?

turns off hot water going to heater in summer to help cool cabin.
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Old 09-24-2018, 08:48 PM
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Tom 35th anniversary
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Originally Posted by cdm747 View Post
Pretty sure that is what that is. If you don't have heat I would suggest you check the blend door actuator. The connector that attaches the arm to the blend door under the dash is notorious for breaking. On my 88 it was the opposite problem though. Heat was on while I was running AC.
I am currently having the same problem......what was your solution?
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Old 09-24-2018, 11:56 PM
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When you vary the auto temp setting between min/max does the blend door rod move?
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Old 09-25-2018, 12:02 AM
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Originally Posted by Rusty Walker View Post
turns off hot water going to heater in summer to help cool cabin.
BS! Read the rest of the post!

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Old 09-25-2018, 07:39 AM
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Originally Posted by Tom 35th anniversary View Post
I am currently having the same problem......what was your solution?
I replaced the broken clip on the blend door where the actuator rod connects under the dash.
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