How to fix vent from turning to defrost?

Asked by Jul 09, 2016 at 09:26 PM about the 2003 Ford F-150 Lariat Crew Cab 4WD SB

Question type: Maintenance & Repair

Dash vent works when at idle or real low speed, accelerate and it goes to
defrost.  If the panel floor button is pushed, then vent works and floor portal
freezes your foot. How can you determine if it's the vacuum lines or the dash
box controller?

1 Answer

56,575

This is going to be a vacuum problem. Intake manifold vacuum is strongest at idle and decreases as you accelerate. There's supposed to be a check valve and possibly a vacuum reserve tank in the system to combat mode fluctuations. The check valve is usually in the vacuum line that runs from the engine, through the firewall, and to the climate control panel on the dash. It will look like a little plastic disk. If you have a vacuum reserve tank (some systems do and others don't) it'll most likely be in the engine compartment and look like a plastic ball or box with 2 vacuum lines connected to it. It may even look like a coffee can with 2 vacuum lines connected to it. HTH. -Jim

Your Answer

Add photo

Related Questions

Search Ford F-150 Questions

Ford F-150 Experts

#1 OJ
OJ
Reputation 6,270
#2 dandyoun
dandyoun
Reputation 3,960
#3 tennisshoes
tennisshoes
Reputation 2,340
View All

Related Models For Sale

Used Chevrolet Silverado 1500
2,625 Great Deals out of 148,536 listings starting at $1,800
Used GMC Sierra 1500
1,154 Great Deals out of 57,810 listings starting at $995
Used Dodge Ram 1500
567 Great Deals out of 12,974 listings starting at $1,200
Used Ford F-250 Super Duty
479 Great Deals out of 42,573 listings starting at $2,995
Used Toyota Tundra
670 Great Deals out of 28,113 listings starting at $1,599
Used Toyota Tacoma
773 Great Deals out of 33,031 listings starting at $1,900
Used Ford Mustang
692 Great Deals out of 38,144 listings starting at $1,750
Used Nissan Titan
214 Great Deals out of 14,522 listings starting at $3,500
Used Ford Ranger
228 Great Deals out of 6,966 listings starting at $1,500
Used Ford Explorer
1,431 Great Deals out of 71,885 listings starting at $985
Used Chevrolet Tahoe
1,068 Great Deals out of 32,278 listings starting at $1,495
Used Chevrolet Colorado
320 Great Deals out of 17,035 listings starting at $2,295
Used Chevrolet Silverado 2500HD
436 Great Deals out of 29,269 listings starting at $2,998

Used Cars For Sale

2017 Ford F-150 For Sale
35,390 listings starting at $17,855
2016 Ford F-150 For Sale
203 Great Deals out of 98,942 listings starting at $17,795
2015 Ford F-150 For Sale
294 Great Deals out of 8,299 listings starting at $18,891
2014 Ford F-150 For Sale
575 Great Deals out of 11,276 listings starting at $9,900
2013 Ford F-150 For Sale
800 Great Deals out of 14,727 listings starting at $7,527