I'm beginning to think there is no WOT relay.

 

The WOT relay has absolutely no control over the HVAC blower motor.

If it appears that the blower is turning off at WOT, then the flow doors are probably just shifting the AC flow from the dash registers to the defroster registers where it is much less noticeable. This is exactly what happens when HVAC vacuum drops toward zero at WOT.

Normally, a vacuum reservoir maintains vacuum to the HVAC controls and Pulse Vacuum Hublock solenoid during short periods of low engine vacuum. If the HVAC vacuum is dropping off at WOT, then there is a leak somewhere in that vacuum system. The Pulse Vacuum Hublock system which was used on 98 to 2000 1/2 4x4's is notorious for vacuum leaks but it could be leaking on the HVAC branch instead.

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If you are still intent on looking for the WOT relay, there are diagrams in your owners manual and in the Ford Wiring Manual for your year Ranger. Be aware that some literature may call it the the "AC Clutch Control Relay" or simply the "AC Relay". Different names, same part.

Again, the WOT relay only affects the operation of the AC compressor clutch, not the HVAC blower.

 

I have this same problem on my 2011. I've replaced all the lines running around the back of the intake manifold as they were extremely brittle. I have the oem shop manual and checked the vacuum canister, just not sure what else to check. Anybody have any ideas?

 

I had a similar problem and the vacuum canister along with the vacuum lines looked good. I went through the diagnostics and it indicated the check valve in the canister was bad. I replaced the vacuum canister and the problem was solved.

I was told that some years of Rangers have an external check valve that can be replaced but I don't have any specific information on that.

 

Problem solved. First, there is no WOT relay, at least not on my 2000, 2.5. If there is a bypass hack please post link.

My AC cutting out on 3/4 to full throttle was loss of vacuum caused by a crack near the end of a small plastic line causing intermittent vac loss. Great description by IN2 FX4.

Cut one inch off, reglued rubber elbow and plugged back in.

 

It's been 12 years and it is doing it again. Time to look for more cracks.