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edhunt0r
edhunt0r, ASE Certified Technician
Category: GMC
Satisfied Customers: 498
Experience:  GM B Tech ASE Certified Master Tech ASE Certified Master Medium/Heavy Truck Technician New Jersey
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I have a 2007 GMC Topkick 5500, it is blowing air out the

Customer Question

I have a 2007 GMC Topkick 5500, it is blowing air out the defrost only. I have checked the vacuum pump and it works fine, also I have found that I am not getting vacuum to the diaphragm that controls the vents. I can manually push it down and the air comes out the vents. Do I have a bad control head or what should I look at next?
Submitted: 6 months ago.
Category: GMC
Expert:  edhunt0r replied 6 months ago.

Hello. Welcome to the site.
Thanks for coming.
I'm ***** *****.
I'm here to provide as much information and insight as I can, to best answer your question.

Can you give me your VIN# ***** I can get the proper information for your vehicle?

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Customer: replied 6 months ago.
1GDE5C1997F421143
Expert:  edhunt0r replied 6 months ago.

Here is the HVAC Vacuum Schematics.

You need to see if you have vacuum at the HVAC control head.

If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.
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Customer: replied 6 months ago.
I have vacuum to the firewall but past that I was not getting vacuum at the control head or at the connection where the black vacuum hose from the pump plugs under the heater box
Expert:  edhunt0r replied 6 months ago.

Then there is a break in the somewhere from the firewall into the cab. Check the connector under the dash.

If you need more help, please use the "Reply" tab to continue our conversation - I'm happy to answer follow-up questions.
If you are satisfied with the information I supplied we would like to close out this question.
If you have no follow-ups at this time, please remember to Rate My Service.

Follow ups are free after ratings, so rate in confidence!
Thank you for posting your question.
Your business is very valuable to us.
Thank You *****

Expert:  edhunt0r replied 5 months ago.

Hi, I'm just following up with you on this question. I provided you with an answer but you never rated my service. You may not understand how the website works. Even though you have been charged by the website the website does not pay me my portion of the charge until you rate my service or reply back to me to let me know that you are satisfied with my help. Please take a moment to rate my service or reply back to me.
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***** *****