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 > Windshield defroster not blowing

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beaubeau

USA

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Joined: 10/24/2006

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Posted: 01/18/22 02:35pm Link  |  Quote  |  Print  |  Notify Moderator

Hi everyone.
We have a 2008 Allegro QBD on the Freightliner front engine diesel chassis.
Last weekend the windshield defroster stopped working. Nothing blows from the ducts under the windshield, where the dashboard and windshield meet.
I’ve ran an endoscope thru as much ductwork as I could, nothing. I suspect a mouse has built a nest in there somewhere….the last time we used the coach furnace, bits of mouse nest were blown out of those coach furnace ducts.

The fan runs, and it will blow warm air from the A/C vents, just nothing up top.

As a backup I’m going to use the anti-fog stuff from Rain-X and I have tiny 12v ‘heater’.

Do any of y’all have suggestions?

Thanks a lot.


Chip & Nancy (and our 3 Shelties and 3 Cavaliers). 2008 Allegro Open Road Freightliner.

Tyler0215

Iowa

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Posted: 01/19/22 08:10am Link  |  Quote  |  Print  |  Notify Moderator

A diverter is not working.

Matt_Colie

Southeast Michigan

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Posted: 01/19/22 09:19am Link  |  Quote  |  Print  |  Notify Moderator

Chip,

I do not know Alegro/Freightliner, but most cab HVAC systems fall into three categories:
Vacuum - not common with diesel because there is no vacuum.
Electric - not popular due to cost
Cable - Not easy to build due to cable routing problems.

I would vote that yours is electric. So, there is an operator at every diverter or control door. Every one of those has a connector that is now 15 years old. I would suggest that you crawl around under the dash and see how many you can find to dis/reconnect and hope one of them gets you.

In the case that it is a cable system, look for a cable that has slipped out of its holder. The holders can usually be crunched a little tighter and the cable pushed back in.

If they did add a vacuum pump to run that and a few other things, I can almost bet that there is one of those stupid little nylon lines that is kinked, or cracked or the rubber connector have gotten cracked.

What ever, you are going to have to find what it is and I can promise that this will not be the last time you have to do this.

Matt


Matt & Mary Colie
A sailor, his bride and their black dog (one is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.


beaubeau

USA

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Joined: 10/24/2006

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Posted: 01/19/22 09:24am Link  |  Quote  |  Print  |  Notify Moderator

Thanks for this very detailed help!

Matt_Colie wrote:

Chip,

I do not know Alegro/Freightliner, but most cab HVAC systems fall into three categories:
Vacuum - not common with diesel because there is no vacuum.
Electric - not popular due to cost
Cable - Not easy to build due to cable routing problems.

I would vote that yours is electric. So, there is an operator at every diverter or control door. Every one of those has a connector that is now 15 years old. I would suggest that you crawl around under the dash and see how many you can find to dis/reconnect and hope one of them gets you.

In the case that it is a cable system, look for a cable that has slipped out of its holder. The holders can usually be crunched a little tighter and the cable pushed back in.

If they did add a vacuum pump to run that and a few other things, I can almost bet that there is one of those stupid little nylon lines that is kinked, or cracked or the rubber connector have gotten cracked.

What ever, you are going to have to find what it is and I can promise that this will not be the last time you have to do this.

Matt


beaubeau

USA

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Joined: 10/24/2006

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Posted: 01/19/22 09:25am Link  |  Quote  |  Print  |  Notify Moderator

Thank you.

Tyler0215 wrote:

A diverter is not working.


diplomatdon

Blaine, WA

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Joined: 08/31/2015

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Posted: 01/19/22 08:40pm Link  |  Quote  |  Print  |  Notify Moderator

Don't know about front engine diesel's but many DP's have a small vacuum pump behind the dash that supplies vacuum to operate heater related options. Could be your situation is caused by broken or loose hoses. Check with Tiffin or ask your question on Tiffin forum. Good luck.

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