1970 300 heater/AC fuse blew but blower motor still operates

Joined
Jul 17, 2020
Messages
173
Reaction score
137
Location
Cleveland, OH
Does the A/C 20 amp fuse only handle turning on the A/C and not the blower motor? If so, where is the 20 amps going to?

So bought car from junkyard 20 yrs ago. Wires looked like spaghetti under the dash with some burnt when I got it. Cleaned up and fixed many connections over the years. Heater has always worked great for years. Blower speed switch never work on high, just low and medium. This is first year I tried to get AC to work. Both wires going to evaporator were cut. I replaced evaporator and fixed wires. First time I used it, I turned it on Max Air. It worked great for about 5 minutes, then I noticed A/C stopped blowing and aftermarket radio turned off and would not turn on. The other A/C and heater button didn't work either. I smelled a very faint burnt smell for only 2 seconds somewhere in the dash. I noticed 20 amp fuse blew, so I took the fuse out but I didn't have one to replace. I started car again, I noticed max air button still didn't work but A/C button worked which I thought was weird without a fuse. Radio works again too. So could the 52yr old A/C wires started to fry before fuse blew which also started to fry the other fuse wires that control the radio which is right below it on the fuse block? Which fuse controls the blower motor? Thanks

IMG_E4282.JPG
 

3175375

Senior Member
Joined
May 16, 2018
Messages
2,600
Reaction score
4,573
Location
Centerville, South Dakota
Does the A/C 20 amp fuse only handle turning on the A/C and not the blower motor? If so, where is the 20 amps going to?

So bought car from junkyard 20 yrs ago. Wires looked like spaghetti under the dash with some burnt when I got it. Cleaned up and fixed many connections over the years. Heater has always worked great for years. Blower speed switch never work on high, just low and medium. This is first year I tried to get AC to work. Both wires going to evaporator were cut. I replaced evaporator and fixed wires. First time I used it, I turned it on Max Air. It worked great for about 5 minutes, then I noticed A/C stopped blowing and aftermarket radio turned off and would not turn on. The other A/C and heater button didn't work either. I smelled a very faint burnt smell for only 2 seconds somewhere in the dash. I noticed 20 amp fuse blew, so I took the fuse out but I didn't have one to replace. I started car again, I noticed max air button still didn't work but A/C button worked which I thought was weird without a fuse. Radio works again too. So could the 52yr old A/C wires started to fry before fuse blew which also started to fry the other fuse wires that control the radio which is right below it on the fuse block? Which fuse controls the blower motor? Thanks

View attachment 540358
You need to get a copy of the Factory Service Manual (FSM). I believe that you can get an electronic copy online (Service Manuals – MyMopar).

For my 69 Fury, the air conditioning blower motor control comes through a separate circuit via the mode control switch. I believe that the 1970 models are the same.


Study it carefully.
 

Gerald Morris

Senior Member
Joined
Mar 9, 2016
Messages
2,328
Reaction score
1,203
Location
Tucson
Does the A/C 20 amp fuse only handle turning on the A/C and not the blower motor? If so, where is the 20 amps going to?

So bought car from junkyard 20 yrs ago. Wires looked like spaghetti under the dash with some burnt when I got it. Cleaned up and fixed many connections over the years. Heater has always worked great for years. Blower speed switch never work on high, just low and medium. This is first year I tried to get AC to work. Both wires going to evaporator were cut. I replaced evaporator and fixed wires. First time I used it, I turned it on Max Air. It worked great for about 5 minutes, then I noticed A/C stopped blowing and aftermarket radio turned off and would not turn on. The other A/C and heater button didn't work either. I smelled a very faint burnt smell for only 2 seconds somewhere in the dash. I noticed 20 amp fuse blew, so I took the fuse out but I didn't have one to replace. I started car again, I noticed max air button still didn't work but A/C button worked which I thought was weird without a fuse. Radio works again too. So could the 52yr old A/C wires started to fry before fuse blew which also started to fry the other fuse wires that control the radio which is right below it on the fuse block? Which fuse controls the blower motor? Thanks

DO get the right wiring diagram first. Many high current loads in these old boats had built-in breakers in the switches. Check that out. I suspect you have plenty bad wiring yet lurking under that dash, and please check that bulkhead connector also! I've been blessed thus far on that note, but saw on our '66 where some wise soul beat me to boring out the main power connection on the bulkhead for straight wiring. You probably should clean all those connections if you haven't already. Do that, to prevent Forest Fires under the dash or hood. Smoky be busy this season!
 
Joined
Jul 17, 2020
Messages
173
Reaction score
137
Location
Cleveland, OH
Thanks 3175375. I have a manual and I've looked at it, but I'm too lazy and stupid to understand it. This car spent 10 yrs sitting outside in a field where it rotted the cowl and water got into the wiriing so is it correct to think that the wires are so bad that they are pulling more amps and blowing the fuse? If I put a meter on the fuse, will it be accurate to see how many amps its pulling? I tried to see if any additional wires were put on that circuit but everytime I start touching wires, something stops working on the dash, then I gotta spend half a day fixing that connection. A fire under the dash already happened before I bought it and fried some wires, so I already did that bulkhead fix and also put in an aftermarket ammeter so full power wouldn't run through the dash. (and OEM one never worked properly anyhow).

I have almost everything working on the dash now so I don't want to tear the whole car apart to put in new wiring. I'm thinking its better to just not use the A/C since it gets over 85 degrees for only about 10 days here? Whose with me!
 

John Kirby

Active Member
Joined
Jun 3, 2016
Messages
282
Reaction score
148
Location
Minneapolis , Mn
The fan and A/C use the same fuse. It does look like there was some monkey business with the wiring at some point. An aftermarket radio is a red flag that the wiring was messed with. I suggest looking at the back side of the fuse panel. There could be some additional wiring added that is incorrect. It's common for the fuse terminals to be corroded so bad they have a poor connection. Take photos so you know where where everything goes. Trace out each affected circuit one wire at a time. They are color coded so it shouldn't be that difficult. Disconnect the battery first.

The blower speed issue could be the switch or wiring going to the blower motor resistor. It's located somewhere on the heater housing where it gets air flow to cool it off. Not sure about the exact details of a '70 model. The service manual is your friend in this situation.
 

Gerald Morris

Senior Member
Joined
Mar 9, 2016
Messages
2,328
Reaction score
1,203
Location
Tucson
Corroded TERMINATIONS result from exposure to the elements, and YES, such will IMPEDE CURRENT! The wire inside the insulation will be FINE, an inch from the terminations, though exposed insulation might be cracked if flexed. Inspect every termination to DETERMINE whether to buy new primary wire for your ride. You can get brand new fuse box and bulkhead connector plastic and brass terminals and put it all together if you can handle reading the old FSM wiring diagrams. Try to replace your old wire with the same colors when possible, for ease of future maintenance. I do. Admittedly, some of the striped wires can be hard to get, but the general colors aren't.

DON'T BUY ANY READY MADE AFTER MARKET GENERIC HARNESS! If you MUST buy a harness, get one MADE FOR YOUR CAR! I do all this wiring stuff myself, as its super easy on pre-1970s cars, and really not too bad until the later 1970s. For re-wiring modern cars, I start with 5 gallons of petrol, some high explosives, and a remote rural location....
 
Top