Doug Lassiter

OK, the a/c on my daughter's 2003 Civic stopped working the other day. Hot day, a/c on and working fine, and then suddenly it's off. No blower. Looking carefully, neither blower or compressor are active. No heat, no a/c no nothing. Have had no troubles with this system before.

I'm reluctant to believe it is the blower switch, because the failure didn't happen when the switch was being turned.

I removed the blower motor resistor/transistor, and it checks out fine. 1500 ohms between pins 3 and 4.

I've checked fuses, though it isn't entirely clear which ones are relevant.

FWIW, the indoor filters were pretty dirty, and I cleaned them out. Maybe that led to the problem?

Where do I go from here? Help appreciated.

cja3455

Check for voltage at the connector of the blower resistor, if no voltage then it is the switch or the wiring/connector else it is the resistor or the motor. The fuses diagram should be in the owner manual

ezone

Pretty common. AC will not be allowed if the blower doesn't run.


There's a lot more to check there. You skipped several steps.

Do you have B+ at the blower motor connector? Fuse is good.

Some might say yes, some say no. I check the cabin filters any time I get a bad power transistor diag.
If you can make the blower motor run by supplying (jumpering) the ground at the power transistor connector (follow a wiring diagram for this) then continue with the rest of the power transistor checks.

Or just open it up and see if it popped it's thermal fuse. That's the usual failure.

Word: http://www.hondasuv.com/members/showthread.php?t=52805

(I have a couple of these that have been redone with a 10 amp fuse just for testing purposes.)


HTH

Doug Lassiter

Good idea. The connector has four wires, blue, black, and a couple of smaller multicolored ones. Any idea which is which?

The fuses diagram isn't much help. The only labels that look vaguely relevant are "cooling fan" (which I have to assume is the engine cooling fan), "condenser fan", and "heater motor". Those are in the under-hood fuse box and are all good. What fuse controls the cabin heating/cooling system? What's it called?

Doug Lassiter

That's important to know. Thanks. I was hoping it was a blower problem rather than an a/c problem.

Do I understand you to mean that checking for 1500 ohms across the power transistor does NOT completely verify that unit? That is, if the thermal fuse is popped it will still show that resistance? How exactly do I check it out and see if it needs to be replaced?

ezone

I said it for a reason. That was the reason.

The link man, click the link.

cja3455

The link has many good info.
Regarding the fuses, I would check all of them it's not supposed to have any blown fuses anyway.
And speaking about blower problems, I know a guy that went and bought the resistor and the motor as soon as his blower stopped working, he replaced the resistor and it didn't work so he replaced the motor and it didn't work either, at this point he returned both parts to the store and he was sure that it was the switch or the wiring, it turns out that it was the wiring connector. That's a nobrainer slightly immoral diagnostic method but it works lol

CraigW

iTrader: (1)

Simple diag test. Lower the glovebox and remove cabin filters and tray. Set the fan switch to on, and at any speed.

Then look in & watch the white fan blades as you 1st turn the key to II and see if the fan spins for a very very short bit. If it spins briefly you have an open TCO on the transistor.

ezone

Swaptronics.

Most reputable suppliers don't allow returns on opened electrical parts.

Doug Lassiter

OK, there is a YouTube online where the guy was saying that the resistance test across the pins on the assembled unit would verify it. But you're saying there is more to it than that. Thanks. That's important.

That being said, I was hoping that there was a way to diagnose the unit without disassembling it (unsoldering connections, etc.) If it works, I sure don't want to damage it! If it doesn't work, I'm happy to pay for a new unit (maybe thirty bucks). So your excellent writeup is how to fix the unit. The question I'm asking is how to check the unit. If I were bringing this into a shop, they'd do the latter, not the former, and they'd charge me a couple of hundred bucks.

There MUST be a straightforward way to check the unit without taking it apart.

Doug Lassiter

OK, did that check. The connector HAS power (blue wire with black trim). It has power no matter how the fan or a/c switches are set. That is, even if they are switched off, the connector still has power.

Is this pointing to the blower resistor as the problem?

(By the way, the light on the a/c button illuminates when the a/c button is pushed, even though the a/c system isn't on.)

ezone

It may pass the resistance test, but the open thermal fuse will stop the blower from receiving any ground when the transistor is turned on.

There isn't any desoldering to take the power transistor apart, simply remove it from the blower housing and pop the plastic shell apart. Ohm check the thermal fuse, it will likely be open circuit.

I think it's actually faster (for me) to do this than to find the books and follow procedures, if you can get the screws out quickly. (I see the exact same failure every time.) It got even quicker after I cobbled up a "repaired" unit just to test with.

Here's a couple links I found with the rest of the checks:

http://home.earthlink.net/~vicrocha/Honda/Honda_index.htm

http://home.earthlink.net/~vicrocha/...Transistor.pdf

ezone

That "power" is coming through the blower motor (also, that fuse is now deemed to be good). It will show as "power" as long as the blower fuse is good and the blower motor is "in circuit".

Your transistor is not controlling the ground to the motor. Yet.

ezone

At the power transistor connector, use a paper clip or something to jumper the thick black wire (chassis ground) to the thick blue/black wire (blower motor ground), this verifies fan will run if it is good.

Paper clip will burn your fingers in a hurry too. 10 amps will turn it into a toaster element.

CraigW

iTrader: (1)

Did you do the test I posted ?? It works.

Doug Lassiter

Yay! Blue-to-blue/black connection makes blower run! (It's not coming out cold though. I assume that's a responsibility of the power transistor.)

Good point that power to that connector means that there are no blown fuses.

I will go ahead and remove the power transistor (thanks for the sheet on that power transistor) and do a check on the thermal fuse. I gather that this check doesn't require any unsoldering.

Doug Lassiter

Did that, and you are PRECISELY right. It spins briefly, and then stops. (Now, you actually can't see the fan blades through the filter tray opering, but I can put my fingers down there, under the filter location, and feel the fan.)

At this point, is it even worth checking the thermal fuse?

ezone

It's actually the responsibility of the HVAC control unit since it looks for a feedback signal from the power transistor and has control over the AC clutch request......but that's not very relevant right now. You bypassed the power transistor.


Pics below are from this link: http://www.hondaaccordforum.com/foru...-repair-40796/

ezone

Nope.
Replace the power transistor.

Doug Lassiter

Hot stuff. Will do. I see I can get one for $30. Will get back to you all to tell you how it worked.

Many, many thanks for all the detailed advice and patience. You guys rock.

Doug Lassiter

Received replacement power transistor and installed it. Everything works perfectly now. As noted, the upper Phillips head screw holding the assembly is a PITA to get to without a highly non-standard screwdriver (and the lower one isn't that convenient either), so I just replaced both of them with hex head screws. Those are easily accessed from the side with a ratchet. Job done. (Well, I suppose I should break into the faulty one and make myself up a spare for a few bucks!) Thanks again for the great advice.

CraigW

iTrader: (1)

Thanks for the update. It should not fail if you keep the cabin filter changed out.

Flex Wilson

ok so im new to this this site and my blower motor was only working on 3/4 but not 1/2 i knew that was the resistor pack but then just two days ago as i'm coming home from school i start to smell wires burning so i pull over shut my blower off and inspect the blowers wires and everything under the passengers dash nothing was on fire looked at fuses and relays nothing seemed bad so i got back in my car to proceed home start the car up then try to turn the heat back on now none of the speeds work next day go to get new resistor pack replaced it still doesn't work someone please help me it's so fing cold outside and i also don't wanna have my windows fog up on me and get me killed.
thank you it's a 1994 civic EX

ezone

Fan motor probably toasted. Test it!

Roll down a window?