Blend door issue I believe

[Whitaker717]

Hi guys, just got done doing a thermostat in the old 87 and when I went to turn the heat on, I have the def function, the heat function, but when I kick it to vent it stays coming out the bottom. I’m guessing a door is stuck or something. Where can I start looking? I hope I don’t have to try to take that dash off. Any help would be great. I did look through some old threads and couldn’t really find what I was looking for. Thanks 

[GonzoTheGreat]

I think that’s the vacuum actuator near your right knee when you’re in the driver seat, that opens the middle vents. 
 

I was able to get the arm back onto the actuator in the girlfriends XJ without pulling the dash. I think I pulled the lower dash though, for visibility. I remember it was quite unpleasant to access, but easier than pulling the whole dash. 

[pizzaman09]

I'd be tempted to suggest you should check for vacuum leaks first, the system defaults to defrost if there is not enough vacuum.

[Whitaker717]

  On 3/1/2025 at 1:32 PM, pizzaman09 said:

I'd be tempted to suggest you should check for vacuum leaks first, the system defaults to defrost if there is not enough vacuum.

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I’m going to take a look today maybe. It’s freezing here where I live. Lol. It’s weird that this just started though by changing my thermostat. Pretty sure nothing got disconnected on accident but I’m not sure. Also strange to me not the other options work and I can hear the blend doors open for those. 

[Pete M]

any vacuum leak in the engine bay will cause what you're experiencing.  check all the hoses.

 

[Whitaker717]

  On 3/1/2025 at 4:33 PM, Pete M said:

any vacuum leak in the engine bay will cause what you're experiencing.  check all the hoses.

 

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I will take a look Pete. I will report back. 
 

[Whitaker717]

  On 3/1/2025 at 5:25 PM, Whitaker717 said:

I will take a look Pete. I will report back. 
 

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I looked at all the hoses and I don’t see any apparent issues. My heat and defrost work just fine. Where is the blend door for the vent? Or actuator. Thanks

[Pete M]

blend door is above the passengers feet.  the cable runs to the temp controller on the dash. 

 

If you've got bubbles in the heater core hoses, that can cause an inability to change temperatures.  if you're still rocking the factory plumbing, the on-off control for the coolant flow is vacuum actuated. 

 

[Whitaker717]

  On 3/3/2025 at 3:42 PM, Pete M said:

blend door is above the passengers feet.  the cable runs to the temp controller on the dash. 

 

If you've got bubbles in the heater core hoses, that can cause an inability to change temperatures.  if you're still rocking the factory plumbing, the on-off control for the coolant flow is vacuum actuated. 

 

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This seems to have started when I did my thermostat I’m guessing. I fixed it and filled it up per the instructions. Everything is still stock. How do I go about getting air bubbles out if that’s what is causing it? 

[Pete M]

is the vacuum line still attached to the valve on the metal spaghetti tubing of the heater core?  does the valve move?

[Whitaker717]

  On 3/4/2025 at 2:51 AM, Pete M said:

is the vacuum line still attached to the valve on the metal spaghetti tubing of the heater core?  does the valve move?

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I will have to get back to you on that one Pete. I can move it by hand but I’m not sure when I switch it to vent if it does. I’ll have to have someone look while I switch it back and forth.