No HVAC while accelerating

[mt hwy]

2005 Sport Trac, A/C, and heat, all seem to back off and not work, or the fan stops working while accelerating. Any thoughts? Thanks.

 

[koda2000]

There is something called a WOT (Wide Open Throttle) relay that cuts out the A/C if you put your foot to the floor. Is this what you're talking about?

 

[rmcalis]

Does the air quit blowing or is it just redirected to the defroster and/or floor vents? I had that problem on my '10, a new vacuum check valve (located under the hood near the firewall on the passenger side) fixed it. Not sure if your '05 has one or not, but would be worth checking into. Mine took a "Motorcraft YG360 Vacuum Checking Switch" (do a google search), yours may a be different part number.

 

[mt hwy]

Thanks for the replies.

Happens during moderate accelerating, and yes, the air flow is diverted to defrost vent on top of dash, and maybe to floor vents. Sorry to not be clear about it initially, I was taking info from my son, then I test drove vehicle and verified that air flow was being diverted - not cut off.

I'll take another look under hood near firewall. Yesterday when I looked seemed like there are the two hoses going through firewall - heater hoses going to heater core? One of them appeared to have a valve in the middle of it. Otherwise, can anyone help me pinpoint where the "vacuum check switch" might be on this 2005 Sport Trac.

 

[koda2000]

When the air flow diverts to defroster vents during acceleration, or when climbing a hill, the problem is vacuum related. DEFROST is the default when when there is little/no vacuum.

 

[N2FORD]

I had a similar problem after my V8 conversion. I had a local shop put a vacuum tank on mine and that fixed it. So I would try to hunt a vacuum issue. Could be a broken hose/line, cracked tank or bad valve like you mentioned. Let us know what you find.

 

[AK NIMROD]

As stated above need to pull the check valve out and test it. You should only be able to blow through on one side of the valve and not be able to suck through the same side. If you can blow through both sides then it's bad. Also look for a broken plastic line. Maybe be broke in the cab or out side where the two lines go through the firewall

 

[swshawaii]

Check valve V8 only?

https://www.amazon.com/Motorcraft-YG360-Vacuum-Checking-Switch/dp/B000C5HZ24

 

[AK NIMROD]

Nope 4.0 has it also, both my rigs have 4.0
Theses hoses are very small look more like wires. Explorers have a gray and black line the gray one goes to a vacuum actuator The other goes to the check Valve then the engine.

 

[AK NIMROD]

Quick photo

 

[AK NIMROD]

Just looked at your Amazon link. I would use it.

 

[swshawaii]

^ Good info, thanks AK NIMROD. Casually looked, but couldn't find it on my ST. Too many 4.0L SOHC configurations. LOL

Happens during moderate accelerating, and yes, the air flow is diverted to defrost vent on top of dash, and maybe to floor vents. Sorry to not be clear about it initially, I was taking info from my son, then I test drove vehicle and verified that air flow was being diverted - not cut off.

May or may not be related, but sounds like similar symptoms, Gen 3 vacuum reservoir behind glove box,.

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