Defrost only
New User
Joined: Mar 2021
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Pulse Vacuum modulator Dorman Part #600-402 located on the passenger side fender of engine bay. When it fails you loose auto locking 4wd hubs and your air system defaults to defrost for safety in winter situations.
Last edited by Parabolst; Aug 1, 2021 at 09:41 PM.
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Joined: Mar 2021
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The ugly thing with the plug on top of it next to the negative battery terminal.
Last edited by Parabolst; Aug 1, 2021 at 09:42 PM.
Hotshot
Joined: Jan 2004
Posts: 19,765
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From: St Louis
It's a loss of vacuum supply to the HVAC control head.
Inspect the vacuum line that runs through the firewall to ensure it is not disconnected or damaged.
A cracked/leaking PVH solenoid body is only one of the potential causes. Cap off the supply to the solenoid and see if your vacuum-powered HVAC functions return or not.
Inspect the vacuum line that runs through the firewall to ensure it is not disconnected or damaged.
A cracked/leaking PVH solenoid body is only one of the potential causes. Cap off the supply to the solenoid and see if your vacuum-powered HVAC functions return or not.
Fleet Mechanic
Joined: Sep 2006
Posts: 1,491
Likes: 295
From: Fresno, CA
The HVAC defaults to defrost so you've likely got no vacuum, or not enough vacuum to move the actuator. I would do the following (in this order):
-Verify vacuum pump is working.
-Verify the vacuum pump cycles off after 20-30 seconds. If it doesn't you've got a vacuum leak somewhere which will require some investigation to find
-If all of that checks out then you'll want to look at the actuator under the dash.
My money would be a vacuum leak somewhere. The 4x4 solenoids are a common item. In the photo above, it's the item next to the fender with a white top. The vacuum pump is the black item to the right of the 4x4 solenoid. The vacuum reservoir is the tank between the vacuum pump & battery.
Spend the $30-40 for a hand vacuum pump. This is very helpful in troubleshooting vacuum leaks.
-Verify vacuum pump is working.
-Verify the vacuum pump cycles off after 20-30 seconds. If it doesn't you've got a vacuum leak somewhere which will require some investigation to find
-If all of that checks out then you'll want to look at the actuator under the dash.
My money would be a vacuum leak somewhere. The 4x4 solenoids are a common item. In the photo above, it's the item next to the fender with a white top. The vacuum pump is the black item to the right of the 4x4 solenoid. The vacuum reservoir is the tank between the vacuum pump & battery.
Spend the $30-40 for a hand vacuum pump. This is very helpful in troubleshooting vacuum leaks.
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Tuned
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From: Wyotana
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This stuff ain't rocket science but you do have to follow directions....
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Tuned
Joined: Dec 2011
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From: Wyotana
Drove it a distance today and noticed I had no cruise control either. Popped the hood and found a rodent nest on top of the Vacuum solenoid. Good place to start!! I'm not going to troubleshoot that mess. I'll make sure the pump is working, then replace the hoses and solenoid.
If I drove the truck more, you'd think I could keep the pests out of it!! Even my cat is on welfare and is too lazy to work!
If I drove the truck more, you'd think I could keep the pests out of it!! Even my cat is on welfare and is too lazy to work!
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