I've taken two 5+ hour (each way) road trips lately. On the return leg of both trips, roughly 5 hours in, the fan stops blowing, and all the vents begin to emit hot air. The van does this regardless of what position the temperate control **** is and what position the vent **** is in. Although putting the **** in Max A/C seems to reduce the flow of hot air to some vents. This obviously is annoying as it's the middle of summer and it's hot outside. If I change the vent **** position, I can hear the vacuum "hiss" behind the dash, so I suspect that system is intact and functioning properly.

While I haven't been able to find much on this specific combination of symptoms, I've found a youtube video implying the blower motor resistor harness needs to be replaced? I did notice one of the terminals appeared to be slightly damaged though I'm not 100% sure.

The blower motor resistor was replaced approximately 2 years ago with a Dorman part.

This is the video I found:
Anyone have a similar issue or other insight for me?

Thanks!

 

The connectors/terminals for the blower motor & resistor are known problems. If any of the terminals for either the resistor or motor appear to be scorched, replace them (post a pic of you’re unsure). Dorman makes a kit that has connector pigtails and heat shrink terminals.

I’d recommend a new blower motor and resistor, as one of them failing tends to cause the other to fail as well.

As for hearing the vacuum hissing when selecting modes, it depends how loud it is.

My experience with a normally operating system has been a very light hissing that lasts only a few seconds (and is easily drowned out by background noise).

I recommend inspecting the vacuum harness in the cab - they tend to sag by the passenger side of the dog house and can get caught by feet/tools/etc - I’ve seen a couple that got pinched in the doghouse as someone else was putting it on.

You should also check the vacuum line from the intake manifold to the check valve for the vac reservoir. They tend to break down over time and can oftentimes just fall off the intake fitting. If you touch it and it feels “crumbly” or you get black residue on your hands, replace it. 2 feet of 1/4 or 3/16 vacuum or fuel line works well.

 

Yup, could only hear the hiss for a second or two when the music was off and stopped at a light. Otherwise it couldn't be heard.

 

The harness looks worse this time around. Though the resistor looks fine.

 

That’s not nearly the worst I’ve seen.

The resistor does look OK but did you check the connection at the blower motor as well? They can have the same problem.

Here’s what you need - Resistor Pigtail - this comes with heat shrink connectors but I recommend soldering if you can.

 

Yeah, I was planning on soldering them.

Connection at the blower is not damaged. Though the Dorman resistor doesn't exactly fit great and doesn't have a satisfying click, but there is no evidence of overheating, arcing or a bad connection there.

I found a new dorman resistor + pigtail for $20 on amazon, might just get both.

I also discovered I mixed up the fuses. I had the swapped a 10A and a 20A fuse, so the HVAC was supposed to have a 20A fuse, but had a 10A. Kind of surprised the fuses lasted as long as they did.

Either way, the harness will be replaced, but thinking I can skip replacing the blower for now.

 

Fuses are generally rated for twice the expected current draw of the circuit. It’s been a while since I’ve tested a blower motor for current draw but I think they’re usually in the 6-8 amp range, so the only reason the fuse swapping didn’t matter is because the blower is [probably] working normally and there’s no other circuit issues.