vanster

Yet another trip to LA and back. My AC keeps going through fuses.
It will run great until I shut off the car and restart it. If I put in a new fuse it will run but it's the second or third on off the seems to blow the fuse. Is this a relay issue?
In 95 degree weather...it gets toasty without it.

dr bob

Which fuse?

vanster

17

Alan

Its NOT a relay issue!

Assume you are using 25A fuses as replacements?

If so it's likely your blower motor is consuming too much power - does it blow the fuse even if you keep it on speed 3 or below?

Alan

dr bob

That fuse supplies the fresh air blower only, via the defrost relay or the fan speed **** and the resistor pack. What is the fan speed set at when you pop the fuse? You can eliminate the defrost option by pulling the defrost relay. Then its just the blower draw through the speed switch and resistor pack.

For those with later cars and blade fuses, there's a handy 30 Amp current meter from Harbor Freight that plugs into the fuse socket. For early car owners with cartridge fuses, you can adapt the H-F meter easily with an aftermarket in-line fuse holder. Need to have at least 14ga and preferably 10-12ga wires. Add a couple alligator clips to the wires so you can connect the wires to the CE panel fuse holder blades.

If you have an IR temp gun, find out if the holder itself is heating due to contact resistance. You have new fuses obviously, but maybe the CE contacts are dirty or corroded enough to heat the fuse and melt it.

vanster

Yes I am using the 25amp blue fuse. When the fuse goes, it changes color from blue to a grey blue, so it must be getting very warm. It never blows once it's on and running. When I shut the motor off, turn off the blower, and AC then when I start up again then turn on the blower it pops it.
This seems to be temp related. As Dr Bob knows driving down Hwy 5 is long and hot. When I stop along the way to get gas the fuse will blow when restarting. Cooler areas like the Bay Area this does not happen.
When I push the the lower lever to defrost the AC blows hard and cold when the fuse is good. It's almost like it over works itself and just gives up. Once it cools off then I'm good for a while.
I've learned to work around this but it would be best to sort it out.

Alan

It doesn't make a lot of sense... Esp that it would happen in hot ambients - from a power perspective at cold startup you'd have a higher voltage => more current in cooler climates.

Are you sure there aren't any aftermarket things attached to fuse 17?

Why do you turn the blower & AC off when you stop the car? there is no need (they won't be active during starting either way). This shouldn't make a difference to this but in this case I think it may (not that its a good solutuion to the issue).

Does the blower ever switch to high speed mode all on its own?

Does the blower performance seem any different in Def mode vs blower switch on full? Does it move any air in the 0 blower switch position?

What is your voltage at the jump post measured with a DVM immediately after a hot restart?

Alan

Alan

What does this mean? this is not consistent with what you have described before... Are you mixing 2 different behaviours here - this implies a temporal recovery failure unrelated to the fuse - please tell us more... and have you already replaced the blower resistor pack for an updated model?

Alan

Randy V

This may help:

https://rennlist.com/forums/928-foru...connector.html

vanster

To answer Alan's questions
Yes the blower will go on intermittently at full blast
It blows colder when in the defrost mode weather or not the AC button is depressed.
Nothing appears to be aftermarket
I have not replaced the blower resistor pack ( was not aware of such a thing)
I just got into the habit of turning things off when shutting the car down.
Like not starting with the clutch depressed or the lights on.
Living in the Bay Area, air con is not used all that much
My heater does not work. Not sure if this is related

Alan

This is "Magic Blower Syndrome" search on that - early cars have a thermal element in the resistor pack that if it overheats will go to full speed fan - the resistor pack is in the aiflow plenum so this cools it.

The fact that this happens means the blower motor is taking too much current
Could be blocked up with debris (in which case speed 0 probably doesn't work (speed 0 is not off - a misnomer)). Alternatively the blower motor has other issues and needs to be replaced.

You can verify by checking the current with a fuse type tester - you will find it is too high.

Def mode selects AC on - regardless of the switch (but it also select full heating)
If you try you will find that the headlights, foglights, blower fan, head unit, cooling fans (more) all turn off automatically when starting - so you don't need to do anything... you can leave it all on.

I always start my car with the clutch depressed.. not sure why you are concerned about this...? Always safer with it depressed no? and the engine has less to spin...

Well its why Def mode seems cool - if it was working it would not seem so cold... It won't have any bearing on anything else here though - most likely a heater valve issue - maybe its been set permananetly closed e.g. wired closed.

Alan