A/C stops blowing when engine is under load

Chimerix · Aug 29, 2014

Aloha all!
So, if I'm accelerating aggressively, or trying to maintain speed when heading uphill, The A/C stops coming out of the vents until the load on the motor is reduced. However, the fan is still blowing, I can hear it. Obviously a dam is closing or opening somewhere. And it exhibits this behavior on Max A/C, but not on regular A/C.

Thoughts?
Mahalo!

James86 · Aug 29, 2014

When the throttle exceeds a certain point, it sends a signal that will disengage the compressor for power. My truck and my friend's 98 do it too. I usually only notice it on WOT.

exbass94 · Aug 29, 2014

Are you sure it's not blowing air out of ANY vents, or is air blowing only out of the defrost vents under high load? Vent selection is controlled by engine vacuum. If there is no vacuum, the system will default to defrost vents only. You will lose most or all vacuum under hard acceleration or heavy loads.

Chimerix · Aug 29, 2014

This is a new phenomenon, at least relatively. We ran the truck for years without this happening, so I don't believe that it's supposed to happen.

James, even if the compressor disengages, that shouldn't stop the fan from pushing air through the vents, right? I mean, the compressor cycles on and off all the time in normal operation.

exbass, I'll keep an eye on it this weekend and see if it's actually closing all vents, or switching to the defrost.

Oh, 1999 Ranger TRS, btw. Extended cab, 4WD.

gw33gp · Aug 29, 2014

This sounds like your vacuum reservoir check valve is not working properly. Under load, engine vacuum drops and the AC/heater vent control can go to default (defroster vent). This is prevented by the use of a vacuum reservoir. Under load the check valve keep the vacuum from bleeding off to the engine.

I had to replace the entire vacuum reservoir because the check valve is inside and can't be replaced separately. I think some Rangers have an external check valve.

kimcrwbr1 · Aug 29, 2014

It has a WOT cutout relay going to the compressor and is controlled by the throttle position senser. It could be at TPS is out of spec telling the computer it is wide open when it is not?

exbass94 · Aug 30, 2014

kimcrwbr1 said:
It has a WOT cutout relay going to the compressor and is controlled by the throttle position senser. It could be at TPS is out of spec telling the computer it is wide open when it is not?

The WOT relay only makes the compressor disengage. It wouldn't cause the blower motor to stop blowing air out of the vents, which is what the OP's problem is. I agree with gw33gp, check the vacuum reservoir and check valve.

deathcyte · Aug 30, 2014

Chimerix said:
Aloha all!
So, if I'm accelerating aggressively, or trying to maintain speed when heading uphill, The A/C stops coming out of the vents until the load on the motor is reduced. However, the fan is still blowing, I can hear it. Obviously a dam is closing or opening somewhere. And it exhibits this behavior on Max A/C, but not on regular A/C.

Thoughts?
Mahalo!

Aloha? Mahalo? Ok which island you on?
Or were on? I'm on maui

kimcrwbr1 · Aug 30, 2014

Not sure on the ranger but my jeep would divert air to the defrosts at the same time it cycled the compressor.

Chimerix · Sep 2, 2014

Ok, went camping this weekend, so there was lots of opportunity to experience this. It is switching to defrost, and the issue is definitely getting more chronic. We've had the truck for around a decade, and living on Oahu with only 597 square miles, we're driving the same roads over and over. This behavior is about 6 months old.

So... I have something called a vacuum reservoir, and it has a check valve. How would I go about locating, identifying, and testing these items? I'm competent to change tires, oil, even brake pads, but I'm not a mechanic.

Also, is this a sign of problems to come?

exbass94 · Sep 3, 2014

The vacuum reservoir is a round, plastic ball located on the passenger side inner fender in the engine compartment. Check out this page:
http://www.2carpros.com/questions/ford-ranger-2006-ford-ranger-heater-adjustment

Chimerix · Sep 30, 2014

Additional info:

The problem only seems to occur when I use the Max A/C setting. On regular A/C, I can push the truck hard for quite a while and the vent never stops blowing cold air.

A/C stops blowing when engine is under load

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