BLS

Hi, I've got a 1989 F150 with a heat/AC fan that only works on high. Today, I pulled the resistor block and found it had a bad thermal limiter (thermal fuse) as I suspected. Does anybody know what the temperature and amperage is so I can get the right replacement fuse? I can't read the markings on the old fuse.

Thanks

bluecar5556

"Low=6A
Med. Low=8A
Med. High=15A
High=25A w/AC" @LLD@T@

My guess is 15 amp would be sufficient, not sure about the temp. though. Fuses rarely blow for no reason. Check the blower and see if it has any electrical resistance by performing a voltage drop with a multimeter across the motor terminals on high speed. If you do not see close to battery voltage across the motor terminals, there is electrical resistance. Spin the wheel and see if it turns freely to check the bearing.

BLS

Hey thanks! You're right on the motor. My bad, I forgot to say it just had a new one put in. The previous owner replaced the motor because it didn't run at all and after that only ran on high. He didn't know what to think after that so he left it. (then sold it to me ) So I'm sure the old motor is what blew the fuse in the first place.

Anyway, I've been thinking. Seems like I remember either hearing about a thermal fuse or replacing it maybe somewhere in the past and it was... 216 degrees? Does that sound right to you? Anybody??? I know I've seen 'em at Radio Shack for coffee pots and they're like... 451 degrees. Seems a little high for this application though. Anyhoo...

Good old Bill

I understand what you are trying to do, perhaps a new blower motor resistor from a junk yard will suffice. Conserving money in todays time is a concern of all of us, but do we really need to reinvent the wheel? If Bluecar can't supply the tech info needed, then its time to change tactics.

bluecar5556

I agree, they didn't put a thermal limiter on resistors that must have air flow across them from the blower motor to keep cool for nothing. Besides, the blower is rated at 25A so the circuit has a 30A fuse to allow for the initial high amp draw spike when the motor is first turned on so using a 15 amp thermal limiter probably would blow very quickly and the temperature rating is what matters most.

Just call me Sean

iTrader: (1)

What thermal limiter? My '72 Pontiac uses a thermal limiter, for the compressor, old technology. The resistor controls fan speed.

bluecar5556

What Ford routinely refer to as a thermal limiter is just a thermal fuse which will go open-circuit when its rated temperature is exceeded. The resistors within the blower motor resistor pack will dissipate considerable heat, so the limiter will be fitted as a safety feature, to minimize the risk of fire.

Sean is referring thermal fuses as being irrelevant, but the blower motor happens to be located under the hood where a fire being started would not be immediately obvious until it's too late unlike the more common blower motors that are located inside the vehicle that do not have thermal fuses.

Either get a thermal fuse capable of carrying more than 20A and < or = 451°F or replace the resistor pack. If you do decide to replace the thermal fuse, use a clip on heatsink so the heat from the soldering iron does not blow the fuse when installing it.

You can always bypass it but if the blower motor ever malfunctions and turns very slowly or not at all on low, med low, med high, there will not be sufficient airflow across the resistors from the blower motor and a fire could ensue. It's fire insurance, up to you.

BLS

Either get a thermal fuse capable of carrying more than 20A and < or = 451°F or replace the resistor pack. If you do decide to replace the thermal fuse, use a clip on heatsink so the heat from the soldering iron does not blow the fuse when installing it.

You can always bypass it but if the blower motor ever malfunctions and turns very slowly or not at all on low, med low, med high, there will not be sufficient airflow across the resistors from the blower motor and a fire could ensue. It's fire insurance, up to you.[/QUOTE]

Yeah, that's what I was looking for. "Either get a thermal fuse capable of carrying more than 20A and < or = 451°F"

I don't think Radio Shack has one like that but there's a lot of electronics shops around so it shouldn't be a problem. Oh, and I would never bypass the thermal fuse for the very reason you stated. Fire!!!

Thanks!