Trucks in default defrost only mode all the time. Im thinking its the vacuum pump. Shouldnt I be able to hear the pump?

 

The buzzing pump sound should be obvious. Pull off the vacuum line from the reservoir. If there is no vacuum present, the pump should be running when the key is on.

 

the vacuum pump on our truck is very noticeable when keys turned on after sitting overnite.

 

Pump doesn't make a sound.
Bad pump? or is there something else I could be missing?

 

like mentioned pull vacume lines off to check for vacume & cycle pump,check for 12v power when pump should be running.

 

you could check fuses. Fuse #27 (15 amp) is the one for pump and auxiliary heater control and brake shift interlock. Have you noticed other components not working too? It's best to resolve pump issue as brakes rely on pump for vacuum since engine doesn't produce it. Here's a pic of connector. Make sure ground is good and power key on run only.

 

I think his truck should have a hydroboost which gets assist from the power steering pump,no vacuum used on these brake systems

 

I thought that was only on the 6.0 setup.... now I'm curious... been a while since I've touched a 7.3 ;-)

thanks Cropharvester! You are right....after 90 something, the electric pumps are mainly for Heater and climate control or engaging front hubs for 4x4

 

You should be able to disconnect the vacuum lines from the vacuum reservoir, then with the vacuum pressure dissipated the pump should run (with key on). If not, then pump is probably bad, though I'd also check fuses.

If pump does run, then there's an abundance of info on leaks occurring at the 4x4 hub seals, or cracked vacuum lines at the front 4x4.

In my case, I have a leak at the heater/ac selector switch. Any leak of the vacuum, anywhere, will cause pump to run continually.

A no-run pump is probably a fuse, bad pump, or indicates that vacuum has been met and the pump has automatically shut off until more vacuum is needed.

 

Fuse 27 is good.
Pulled vacuum line to the res with key on and cycled 4x4 switch and HVAC controls. No pump sounds.
Then checked for power at the pump. It has power.
Looks like Im replacing the vacuum pump. Should I go with OEM or will Advanced Auto be sufficient?
Thanks for the help guys.

 

I see Advance has the Dorman for $85. Rock Auto lists it for $51. You can find discount codes online for Advance and maybe get close to Rock's price.

 

advance auto will match rock auto price if same part

 

Oh, sweet! I didn't even think to ask them if they'd match. That would sure beat waiting for shipping.

 

i had a issue up there with a new guy selling me wrong part and the guy that knows me tried to make mends and pulled up a screen for price match and rock auto was on the list just make sure to bring proof of price and make sure its exactly the same part numbers and supplier and you should have no issue , now i know he can do this i hit him with it all the time lol

 

I should have checked my thread sooner.
Couldn't wait for shipping and paid full price. $90.
Good news is it fixed my problem.
Thanks FTE