AC cuts off when accelerating

[Lemarque]

Searched but didn't find anything that described the following:

Cruising, the AC works fine. Under even slight acceleration the fan stops; that is no forced air from the vents. Backing off the gas, the fan starts blowing again with cold air. Driving country roads with even gradual uphill stretches is a real pain in NM when the AC (fan) stops. So I'm guessing that somehow the fan is in some circuit with the AC?; but I'm only guessing.

Any help appreciated.

2008 FX4

 

[rusty ol ranger]

You sure its stopping or is it switching to the defrost vent?

I had an Econoline that would do that and it would blow out the defrost. It was a vacuum issue somewhere...never figured out where.

 

[Alan_nc]

Isn't the AC supposed to shut off under acceleration? Sounds like yours is a bit sensitive. Just for comparison does the fan shut off when you have the heat on and accelerate?

 

[Lemarque]

Thanks guys.

Driving this morning with just the fan on (no AC) it behaved the same. No fan under acceleration.

Scheduled Monday for some minor work with my mechanic and I'll ask him to troubleshoot for a vacuum leak unless someone relies with additional info.

 

[RonD]

You are loosing vacuum in the cab when accelerating, common issue

In the engine bay there will be a grey and a black hard plastic vacuum lines coming out of firewall on passenger side
Black one is the main line and runs forward to the Vacuum reservoir in the lower front of engine bay

This black line cracks or is melted by exhaust

 

[Lemarque]

You are loosing vacuum in the cab when accelerating, common issue

In the engine bay there will be a grey and a black hard plastic vacuum lines coming out of firewall on passenger side
Black one is the main line and runs forward to the Vacuum reservoir in the lower front of engine bay

This black line cracks or is melted by exhaust

Thanks RonD - Probably saved me a good bit of cash in troubleshooting.

Not the best pic, but I'm really enjoying my second Ford. First was a 57 Ranchero I bought at auction 30 years ago.

 

[Ranger850]

You sure its stopping or is it switching to the defrost vent?

I had an Econoline that would do that and it would blow out the defrost. It was a vacuum issue somewhere...never figured out where.

I drove an E-350 with the same issues. It was a work van, so nothing ever got fixed on that beast.

 

[Dirtman]

As Ron said, vacuum issue. Same problem with my truck but was a broken check valve. Engines don't make vacuum under acceleration and vacuum is what holds the vent controls in position so if you loose vacuum it switches to defrost. (Default mode spring operated). The vacuum reservoir stores vacuum so you don't loose control of the vent position, but with a leak or bad check valve, it magically disappears when you hit the gas.

 

[Uncle Gump]

I will say however... a vacuum leak is one thing causing the air to not blow out the right place... if the fan completely stops working... that is an entirely separate issue. The fan should continue to blow...

 

[gw33gp]

I agree with Dirtman. It seems like the fan shuts off but the air is just directed to the defrost vents as a default and it just seems like the fan shuts off. I had to replace my vacuum reservoir because the check valve went bad. It was a pretty easy fix on my 02. I suspect an 08 would be similar.

 

[Lemarque]

I drove an E-350 with the same issues. It was a work van, so nothing ever got fixed on that beast.

Yeah well, if your wife had to drive it, it would have gotten fixed

 

[Lemarque]

I will say however... a vacuum leak is one thing causing the air to not blow out the right place... if the fan completely stops working... that is an entirely separate issue. The fan should continue to blow...

<thud> The fan stops completely. So what would cause this?

 

[Lemarque]

I agree with Dirtman. It seems like the fan shuts off but the air is just directed to the defrost vents as a default and it just seems like the fan shuts off. I had to replace my vacuum reservoir because the check valve went bad. It was a pretty easy fix on my 02. I suspect an 08 would be similar.

Doesn't seem to be coming from the defrost vents. Fan stops completely.

 

[Uncle Gump]

I'm not sure where you would go from there...

Are you positive it doesn't just switch the coming out of the defroster?

 

[Lemarque]

I'm not sure where you would go from there...

Are you positive it doesn't just switch the coming out of the defroster?

I'll double check tomorrow but I reached over to the windshield this morning and didn't feel anything.