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Old 09-16-2020, 09:15 AM   #1
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Winnebago or Workhorse: Blue Vacuum Line Under Hood

I'm not sure if this is a Winnebago/Itasca or Workhorse forum question. In another thread, I've been trying to sort out a AC issue, so I was looking around under the hood yesterday. I noticed a blue wiring or vacuum line that was partially rotted away. After further inspection, I believe it's some sort of vacuum line. The lines starts from an unknown (to me) part and feeds through the firewall. As I touched the line, it literally crumbled apart even more. I'm guess it's deteriorated from engine heat. I haven't tried to see from inside the coach where it might go.

Pictures are of the line and part where it originates and into the firewall. The part picture was taken from the passenger side tire well from underneath.

Could anyone tell me what the part is, where it's gong and what it's for?

Thank you. -RT
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Old 09-16-2020, 09:20 AM   #2
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I believe that vacuum line operates the vacuum controlled "door" in the heater/AC that switches the flow of the output air from the floor to the defrosters. Hopefully, someone will come along with a more definitive answer.
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Old 09-16-2020, 09:36 AM   #3
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Yes, it’s for your Ac/Heater door. Just buy a piece of 1/8” vacuum hose from AZ and replace the bad section. The blue hose will fit inside the replacement vacuum hose like a glove. No need to clamp, just slip it in a couple inches. Just a pin hole will keep it from working.
Go down to 3rd drawing That hose travels from the actuator you have pictured, thru the rubber grommet, then to back of heater control. Must be a common problem as mine was same way.
https://winnebagoind.com/resources/s...g%20&%20AC.pdf
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Old 09-16-2020, 11:20 AM   #4
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Yes, it’s for your Ac/Heater door. Just buy a piece of 1/8” vacuum hose from AZ and replace the bad section. The blue hose will fit inside the replacement vacuum hose like a glove.
Thank you very much for the info. I suspected it might have something to do with the HVAC. I run the AC far more than the heater so I guess I didn't comprehend that the door isn't completely functional. Plenty of air flows through the dash vents. But I have seen that when I turn on the heater and fan at full blast, I can see the dash mat move from air flowing from the defroster vents when it should only be down under the dash near my feet. I certainly hope the rot doesn't go all the way up to the firewall!

I'm not very savvy on these things and was wondering if you could tell me what the part is that the vacuum line plugs in to. What is it?

Thank you. -RT
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Old 09-16-2020, 11:59 AM   #5
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I believe they consider it a vacuum motor. Basically it’s just a air cyl with a diaphram piston. Apply vacuum to 1 side, the piston moves and thus the linkage to the door moves. No need to mess with that ‘motor’ just splice in a new section of hose as long as you have enough on the outward side of the large rubber boot/plug. This particular blue hose controls your MAX AC temp. . With the hose bad, the door won’t close for MAX AC cooling.
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Old 09-16-2020, 12:38 PM   #6
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I believe they consider it a vacuum motor. Basically it’s just a air cyl with a diaphram piston. Apply vacuum to 1 side, the piston moves and thus the linkage to the door moves. No need to mess with that ‘motor’ just splice in a new section of hose as long as you have enough on the outward side of the large rubber boot/plug. This particular blue hose controls your MAX AC temp. . With the hose bad, the door won’t close for MAX AC cooling.
Again, thank you for your informed replies! -RT
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Old 09-17-2020, 04:29 AM   #7
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Hummmmmmmmmmmmmmmmmmm......
Possibly looks like rodent teeth marks on this hose.
The plastic seems to attract rodents, something in the plastic that they like to eat.
Very common failure mode for hoses and wires.
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Old 09-17-2020, 05:49 AM   #8
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I had to replace my blue vac line about 8 yrs ago. Take a sample of the blue line with you to the auto parts store. Buy the "repair kit", it will have the fittings you need to splice into the blue line just before it goes into the firewall and over at the vacuum valve.
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Old 09-21-2020, 10:26 AM   #9
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That blue hose operates the reciculate door when you put the AC to Max AC. When it leaks you loose all vacuum and the vents automatically default to defrost. The other end goes to the vacuum switch on the HVAC control panel. It happened on mine and I just ran a rubber line where it was bad. I think it's a heat and also that it rubs on the firewall when you are driving.
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Old 09-22-2020, 04:13 PM   #10
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I haven't been able to make a repair but did spend a little more time looking around. The blue hose is 'dry-rotted', most likely due to the engine heat. Far more of the line is damaged than what I originally thought. I might have a couple of inches at the top before it goes through the firewall to work with at best. I found the two lines (One blue, one green) under the dash, running to the back of the HVAC switch. It doesn't look like I can remove that switch without pulling the stereo too as it's blocking access to the mounting screws, which are mounted on the inside of the dash switch. I'd also have to deal with the thick wire sealant at the firewall. I'm hoping that there is enough good vacuum line at both ends to make an easy repair but something about this motorhome always turns into Murphy's law.

Strangely, when I ran the HVAC, even though there is nothing left really of the vacuum line, every 'vent' position worked as it should. Air flowed from the proper vents when using defrost / heat / vent and AC modes. I'm certainly confused on that one if the blue vacuum line actually operates the heater door.

Also, the second line is green that runs from the inside HVAC switch. Where does that go (exits out the firewall with the blue line) and what purpose does it serve?

Thank you.-RT
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Old 09-22-2020, 04:31 PM   #11
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Your dash control gets vacuum from the engine intake manifold, so the green could be the supply line, blue line would only leak vacuum when recirculating ( max A/C) is selected.
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Old 09-22-2020, 06:15 PM   #12
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I haven't been able to make a repair but did spend a little more time looking around. The blue hose is 'dry-rotted', most likely due to the engine heat. Far more of the line is damaged than what I originally thought. I might have a couple of inches at the top before it goes through the firewall to work with at best. I found the two lines (One blue, one green) under the dash, running to the back of the HVAC switch. It doesn't look like I can remove that switch without pulling the stereo too as it's blocking access to the mounting screws, which are mounted on the inside of the dash switch. I'd also have to deal with the thick wire sealant at the firewall. I'm hoping that there is enough good vacuum line at both ends to make an easy repair but something about this motorhome always turns into Murphy's law.

Strangely, when I ran the HVAC, even though there is nothing left really of the vacuum line, every 'vent' position worked as it should. Air flowed from the proper vents when using defrost / heat / vent and AC modes. I'm certainly confused on that one if the blue vacuum line actually operates the heater door.

Also, the second line is green that runs from the inside HVAC switch. Where does that go (exits out the firewall with the blue line) and what purpose does it serve?

Thank you.-RT
Did you look at the link I posted in post #3? It shows what the blue and green hoses are for, where they go, as well as what each of the dash knob positions controls. A couple minutes studing the 3rd diagram and the chart will give you a clear understanding on what does what. The reason you feel that all the dash selections are working ok, even with the blue hose compromised, is because the blue hose closes the outside vent door for MAX AC, as has been stated a couple of times. You still will get airflow with the bad hose, it'll just be mixed with outside air, as well as not close the water valve since the Blue and green share the same vacuum port.

If you have 2" of good hose still length still exposed, thats plenty to slip a new section of vacuum hose over the old piece. You may be able to pull a little more of the blue hose out of the rubber groumet. Been there, done that. You could always smear a film of silicone over the old tube to 'glue/seal' the new hose, if you wish. No need to remove radio.
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Old 09-23-2020, 11:38 AM   #13
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Did you look at the link I posted in post #3? It shows what the blue and green hoses are for, where they go, as well as what each of the dash knob positions controls. A couple minutes studing the 3rd diagram and the chart will give you a clear understanding on what does what. The reason you feel that all the dash selections are working ok, even with the blue hose compromised, is because the blue hose closes the outside vent door for MAX AC, as has been stated a couple of times. You still will get airflow with the bad hose, it'll just be mixed with outside air, as well as not close the water valve since the Blue and green share the same vacuum port.

If you have 2" of good hose still length still exposed, thats plenty to slip a new section of vacuum hose over the old piece. You may be able to pull a little more of the blue hose out of the rubber groumet. Been there, done that. You could always smear a film of silicone over the old tube to 'glue/seal' the new hose, if you wish. No need to remove radio.
Thanks once again for the great info! I did look at the diagrams but you give me too much credit if you think I understand that stuff. I definitely had a different understanding regarding why the heater door would not operate correctly and the end effect.

I'm going to AutoZone to get the hose and hope to repair it this weekend, I time allows.

Thanks again for all the info...

Now, how much do you know about the 2005 Norcold refrigerators used by Winnebago?? -RT
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Old 09-23-2020, 01:26 PM   #14
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Hummmmmmmmmmmmmmmmmmm......
Possibly looks like rodent teeth marks on this hose.
The plastic seems to attract rodents, something in the plastic that they like to eat.
Very common failure mode for hoses and wires.
While that could be, I'd bet money the hose is dry rotted. I replaced that same vacuum line on our 03 model a few years ago. The funny thing is, it was only dry rotted in one small section, I think about 6 inches long if I remember correctly. The rest of the line was flexible and appeared to be in good shape. I went ahead and replaced it all anyway.
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