Hot air blows when motor is under strain

Asked by Dec 28, 2016 at 05:52 PM about the 1999 Dodge Ram 1500 4 Dr Laramie SLT Extended Cab SB

Question type: Maintenance & Repair

Anytime the motor on my truck is under
strain- climbing a hill, "punching" the
accelerator- hot air starts coming out of the
vents. This happens when I just have the
vent blowing or even when the ac is on.
Sometimes letting off the accelerator will
make it go back to cool and other times
you have to turn the blower completely off
for a minute and then turn it back on to get
the cool air to blow again. Engine is 5.3L
V8. Any ideas on what would cause this?

3 Answers

28,995

It might be a vacuum actuator on your model, I'd have to look that up, but this type of problem was common back in the era of vacuum actuators. You put the engine under heavier load, and it can't produce enough vacuum, so some actuators move - in your case, the temperature blend door is opening to the heater core. Then when you let off, it moves back. A bigger vacuum reservoir can help, you can also get some aftermarket setups that run off the battery.

86,245

I suspect a leaking vacuum hose. Check the hose that goes to the vacuum tank. My F150 did the same thing and it was just a hose that had rotted off.

28,995

FoR, that's probably just it, a leaky vacuum line. When engine vacuum drops, combined with loss of vacuum from leak, the actuator moves. Thanks for clarifying.

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