Diagnosing a Heat Won't Blow Fan Problem

blower vents
Fix your heater blower and these vents will reward you with warmth, or coldness. Getty

Even if your car heater system isn't working well, the good news is it will usually work a little. If you're one of those picky drivers who isn't satisfied with something working only a little, read on. This question came in from a reader who was having a problem with their car's heat. One of the most common problems with an automotive climate control system is a lack of blower pressure, or no blower at all.

That means a trickle out of your vents instead of the rush you asked for. When it does happen, you're left with a miserably underpowered heat or AC system. It will still work with no fan, and you'll usually still be able to control the temperature of the air that is blowing, or tricking, out. But a climate control system with no fan to push the air around is anything but controlled. You want your fan back, I get it. And so did the author of this letter. Check out what he's been through, and why he should've asked an expert from the start! Here's what he wrote:

Vince, My problem is on a 1996 Dodge Caravan 3.3 liter. It has A/C but is a short body and has no rear heat or A/C. The trouble relates to the blower motor and its activation. My blower motor does come on. The Haynes manual says the blower is activated by a relay. I need to find the location of this front blower relay and the fuse that powers it.

I work in the telephone business and am very familiar with DC wiring. Haynes say it is located in the PDC under the Hood, along with a 40 amp blower fuse in the PDC. Dodge owners manual shows the 40 amp blower fuse, #25, but does not mention any blower relay in the PDC.

All the relays in the PDC have designated legends on the cover, but none indicate they are for the front blower relay. Haynes also states this blower relay is powered via a fuse in the junction box from under the dash, #12, 10 amp. The Dodge owner's manual contradicts this and shows no 10 amp fuse for the purpose of a blower relay, inside the junction box.

Actions so far:

  • Checked the blower with direct power and it works. 
  • Checked for incoming resistance ground to the blower, from the dash control switch and it works. 
  • Checked for battery at the blower, when the car is running. There is no battery to operate the blower 
  • Rotated all the PDC relays around, they have the same ID, other than ABS pump. Blower still does not work 
  • Rotated all the unmarked relays around in the junction box. Blower still does not work. 
  • Checked continuity of 40 amp blower fuse, it's okay. 
  • Checked most fuses for continuity in the PDC and Junction Box and they are okay.

Note, there is no burnt or corroded wiring. I just have to find the blower relay and its fuse. Can you help?

Thanks in advance...

A. In the case of this Dodge's blower, the answer was not at all tough. The Front Blower Motor Relay (also known as the AC Relay) is behind the junction block with a black connector, B05. The relay is the culprit. This is often the case. Your vehicle should have a complete relay diagram showing the location of all of the vehicle's electrical components, like fuses and relays.

If your owner's manual is incomplete, you should definitely buy a proper repair manual. Sadly, even the Haynes manual can fail you. The best repair manual is always a factory manual, but these can be either hard to find or many times more expensive than a "consumer friendly" repair manual. That said, if you get your hands on a high-quality manual, there are far too many times than you'll be able to count that you'll thank yourself for buying it. 
To fix any blower, the first things to look at are the fuses, relays, and electrical connections. All of these are fairly easy to check. You did this, but without all of the info you needed, the electrical troubleshooting project you set out on was destined to fail.

 

This article was edited by Matthew Wright

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Wright, Matthew. "Diagnosing a Heat Won't Blow Fan Problem." ThoughtCo, Sep. 13, 2016, thoughtco.com/heat-wont-blow-fan-problem-4086396. Wright, Matthew. (2016, September 13). Diagnosing a Heat Won't Blow Fan Problem. Retrieved from https://www.thoughtco.com/heat-wont-blow-fan-problem-4086396 Wright, Matthew. "Diagnosing a Heat Won't Blow Fan Problem." ThoughtCo. https://www.thoughtco.com/heat-wont-blow-fan-problem-4086396 (accessed November 18, 2017).