Heater resistor plug - Chevelle Tech
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post #1 of 4 (permalink) Old May 19th, 14, 1:38 PM Thread Starter
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Mike
 
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Heater resistor plug

Hi Folks,
This is my first post, I have a 72 Sprint that I have been working on over the last 5 or 6 years,It sat for 14 years before I bought it.

I removed the sweep dash just after buying it to replace the heater core, never reinstalled it due to starting the rust repairs and so on, mean while I picked up a Monte Carlo Dash, Yesterday I found time to install it, all went ok but apparently the wiring harness that came with it is from a non- a/c car, My Sprint has Factory air.

Everything else on the harness fell right into place.

My question is : the existing wiring harness has the T plug for a resistor for non air cars, Do I need to get a different wiring harness, modify this one, or is something I do not need to worry about?

Thanks, Mike
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post #2 of 4 (permalink) Old May 19th, 14, 4:09 PM
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Bob
 
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Re: Heater resistor plug

The 70-72 Chevelles with factory A/C have a STAND ALONE wiring harness. It enters the dash above the Dist. Also What ever under dash and under hood harness you are using.
You need the SAME YEAR - A/C harness. Whats the big deal !
I built a driver it is a 1971 Nomad Wagon with factory A/C. I installed a green 70 SS Dash, With the 70 under dash harnsee and a 70 under hood harness.
NOW I am driving the car and want to get the A/C working.. CLUE:
1971 Chevelles with Fac. A/C have relays under the glove box. 1970 Chevelles with Fac. A/C -DO NOT. Now I am having an OH SH!T Moment.
I enjoy working on A/C, I have done it for years. YES,,,, You can make anything work if you have the time money and knowhow.
Just to keep it all FACTORY and have all the wiring the same. I installed a 1970 A/C wiring harness.
NOTE: 1971 Chevelles with A/C. After the key is shut off and in your hand...... LISTEN.... You will hear a click.... What is it?
My 1971 Nomad wagon with a 307 and A/C. Like I said " After the Ign. is shut off and the key is in your hand, You will hear a click? "
This click is a relay under the glove box (with the key in your hand) It sends 12 Vts. to ENGAGE the A/C Clutch to Load down the engine, WHY?
This EXTRA LOAD on the engine without the Ign. on, Acts as a "ANTI DIESELING UNIT". This is an item 70 Chevelles do not have.
Another reason not to mix and match wiring harnesses.
Bob
P.S. Not sure ,, But I think a 70 A/C harness is a 5 wire and a 71 is a 6 wire, Not sure, I do not remember?


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post #3 of 4 (permalink) Old May 19th, 14, 5:57 PM Thread Starter
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Mike
 
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Re: Heater resistor plug

Bob,
Thanks for the reply, In further checking I may have found my answer but not sure yet, From what I am finding the non a/c harness used a 4 prong T style plug for the blower switch, the a/c harness uses two 3 prong plugs side by side on the 6 terminal a/c ,heater blower switch.

I have an original 1972 GMC Sprint shop manual, parts book & fisher body service manual, but you have to pay attention to what they do not tell you. Not much info on the round gauge dash or A/C wiring. The parts book does list 2 different blower switches, 1 non A/C , 1 A/C.

I have an extra A/C harness, it is separate as you thought. If I use my test light at the blower relay that is mounted on the Evaporator housing I have power on the inline fuse to the relay, if I jump across the relay then the blower fan will run.

I guess I am lost as to how the 12 v is supplied to the blower switch, I am thinking the power is supplied through the relay on the Evaporator case and then routed on the A/C Harness to the blower switch.
There are no relays under the dash, no clicks from the clutch disengaging as no power there yet.

I if I need to find a factory harness from a 71 / 72 w A/C then that is what I will do, I do not have time for jury rigging / butchered up wiring harnesses.

Thats where I am now, Thanks again for the reply.

Mike
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post #4 of 4 (permalink) Old May 20th, 14, 7:28 PM
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Joe
 
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Re: Heater resistor plug

Quote:
Originally Posted by M Zeigler View Post
Bob,
Thanks for the reply, In further checking I may have found my answer but not sure yet, From what I am finding the non a/c harness used a 4 prong T style plug for the blower switch, the a/c harness uses two 3 prong plugs side by side on the 6 terminal a/c ,heater blower switch.

I have an original 1972 GMC Sprint shop manual, parts book & fisher body service manual, but you have to pay attention to what they do not tell you. Not much info on the round gauge dash or A/C wiring. The parts book does list 2 different blower switches, 1 non A/C , 1 A/C.

I have an extra A/C harness, it is separate as you thought. If I use my test light at the blower relay that is mounted on the Evaporator housing I have power on the inline fuse to the relay, if I jump across the relay then the blower fan will run.

I guess I am lost as to how the 12 v is supplied to the blower switch, I am thinking the power is supplied through the relay on the Evaporator case and then routed on the A/C Harness to the blower switch.
There are no relays under the dash, no clicks from the clutch disengaging as no power there yet.

I if I need to find a factory harness from a 71 / 72 w A/C then that is what I will do, I do not have time for jury rigging / butchered up wiring harnesses.

Thats where I am now, Thanks again for the reply.

Mike

Mike,

Yes, your best bet is finding the correct harness.

Completely different set-up for A/C and non-A/C.

The A/C switch allows the blower to remain on LO even when it is in the "OFF" position IF the A/C is "on" so things don't freeze up. The power from the dash is sent into the A/C harness connections and split between the compressor activation feed switch and the fan speed control switch. A/C fan switch "HI" sends 12 volts out to the relay mounted on the evap. box on the firewall. This is only a trigger to allow full 12 volts from the horn relay directly to the blower fan. All other speeds are accomplished by the switch sending power to the evap box's resistor assembly to drop voltages for various speeds. Resistor is underhood, vs. under-dash with the HEAT only set-up.

-If you don't stand for something, you'll fall for anything.
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