No blower motor under engine load

[MankDeems3.0]

Hey all, owner of a 99 XLT 5 Speed. Under heavy engine load my blower motor shuts off. I know the AC clutch is supposed to shut off under load but this applies to my heat

For example I take the interstate home and in 4th gear at 3500 I have no blower fan and 5th gear it comes back unless I put the engine under load.

Any suggestions on vacuum leaks or speed sensors I need to look at? HVAC for dummies books? Thanks

 

[avid]

Sounds like the vacuum reservoir. I had to replace mine a couple years ago and it fixed the issue.

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