Author Topic: A/C  (Read 13924 times)

Offline brlarl

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A/C
« on: July 22, 2012, 06:09:16 PM »
I swapped the complete engine, tranny, and  wiring harness out of a 1990 Chevy Suburban into a 1985 c-10.  I drove the truck around for about 2.5yrs with no problems at all but I parked the truck in a garage for about 2 yrs.. Now that I'm wanting to sell the truck the A/C system will not power up. I have no power at all to the blower. I found a few burnt wires at the relay and replaced the harness and the relay. I also had a few burnt wires at the dash control so I changed both harnesses. (soldered all the harnesses)I changed the resistor as well as the firewall relay (I think it controls the compressor). All the fuses are good under the dash but I do not have 12V at the dash control at either harness. I do have 12V at the relay mounted near the blower but nothing happens from there. Can anyone share any ideas on my problem? Are there any fusible links for the a/c system on a 1990 Suburban? Any help would be great I need to sell the truck soon and want to fix this before I do to make sure I get top dollar for the truck. Thanks Guys
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Offline 78 Chevyrado

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Re: A/C
« Reply #1 on: July 23, 2012, 01:08:30 AM »
Open up the new relay you installed and check for a burnt up resistor inside.  if it IS burnt up, return it, buy another one, and BEFORE installing it snip out the resistor and use it like that. (the same one that burnt up in the other one.)

I had this on my truck, took 3 relays before i figured it out.  turned out the replacement relay had an extra resistor the stock relay did not and every time I turned it on it burnt up the extra resistor.  I snipped it out of the last replacement and it works perfectly.  if you do snip the resistor, make sure whats left doesnt contact anything it shouldn't like the case, etc.
Kenny

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Offline brlarl

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Re: A/C
« Reply #2 on: July 23, 2012, 07:33:58 AM »
I did open the relay but did not notice if there was a resistor in there but I will check again today.  Thanks.  Any other input out there?  Thanks Guys
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Offline brlarl

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Re: A/C
« Reply #3 on: July 23, 2012, 08:22:41 PM »
78Chevyrado this is what I have in the relay, is this what you speak of or is this a diode? Thanks
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Online bd

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Re: A/C
« Reply #4 on: July 23, 2012, 08:52:58 PM »
That's a clamping diode.  The end of the diode with the little silver band should be connected to the positive (+) terminal of the relay control circuit.  If the silver band is connected to negative (-), the diode will pop like a fuse when the relay is energized. 

The purpose of a clamping diode is to prevent the relay coil from 'spiking' the control circuit with high voltage when the relay is switched OFF.  It protects switches and electronics.
Rich
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Offline brlarl

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Re: A/C
« Reply #5 on: July 23, 2012, 09:06:16 PM »
bd do you have any ideas about what my issues could be caused by if this relay does not have any resistors 78 Chevyrado speaks of? I have 12Vat the relay going in but nothing coming out or at the dash switch. All fuses are good. Thanks
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Online bd

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Re: A/C
« Reply #6 on: July 24, 2012, 01:09:20 AM »
Allow 78 Chevyrado some time to respond to your post of the relay pic.  Not everyone is on the forum everyday.  In the meantime...

...I have no power at all to the blower.  I found a few burnt wires at the relay and replaced the harness and the relay.  I also had a few burnt wires at the dash control so I changed both harnesses (soldered all the harnesses).  I changed the resistor as well as the firewall relay (I think it controls the compressor).  All the fuses are good under the dash but I do not have 12V at the dash control at either harness.  I do have 12V at the relay mounted near the blower but nothing happens from there....

If the wire connections to the selector and blower switches in the control panel were burned, chances are the switches are damaged as well.

Not sure, but I'm going to assume that your A/C wiring is similar to an '85-'87 square. 
You state you have no power anywhere except at the blower relay (I presume on the 10-ga red wire).  Look behind the instrument panel in the area to the right of the steering column... there should be a ~16-14-gauge solitary brown wire feeding through a single-wire connector.  This should be the power lead that feeds your A/C selector and blower switches.  This brown wire comes directly off the 25-amp Heater-A/C fuse in the fuse block.  Use a test light and probe the brown wire for 12-volt ignition power.  Check the in-line connector & terminals for heat damage.  If the circuit is dead, probe both sides of the Heater-A/C fuse.  Then, give us an update.
Rich
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Offline brlarl

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Re: A/C
« Reply #7 on: July 24, 2012, 07:45:10 AM »
I forgot to mention that I did change out the switches.  I noticed that brown wire you mentioned last night when I was sitting in the truck starting at the dash.  I did check it for power but I'm so caught up in fixing it that I do not remember if I had the key turned on.  I do remeber that there was no power so either the circuit is burned from the fuse box up or I did not have the key turned on!  Either way I will check it again tonight with the key ON and report back.  LOL  :o  Thanks BD for your input it is much appreciated!
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Offline brlarl

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Re: A/C
« Reply #8 on: July 24, 2012, 06:02:01 PM »
Ok I tested the wire to the right of the cluster.........no power detected.  I traced the wire to the fuse block and no power on either side of the fuse. I traced the wire that tied to the hot side of the fuse and followed it to the ignition starter switch and found the the wire harness and switch had burned. I replaced the switch and harness. Now I have power at the selector switch at the dash but nothing on the speed selector. I still have power on the red 10g wire at the relay mounted on the box near the blower but the blower does not kick one. also the blower does work as I jumped it directly to 12V. Any ideas? Thanks
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Online bd

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Re: A/C
« Reply #9 on: July 25, 2012, 01:15:50 AM »
Here's the skinny on how the blower circuit works.  Read through it while you're "looking" at the wiring in your truck, or the details will probably put you to sleep  ??? :

You stated you restored power to the selector switch, via the 16-ga brown wire from the fuse block...

There are two additional 16-ga brown wires connected to the selector switch, each has a single white stripe.  One of the brn/wht wires attaches directly to the blower resistor (bypassing the blower switch) to power the blower motor with constant low speed; hence, low fan speed is not controlled by the blower switch.  The other brn/wht wire feeds the blower switch with 12 volts.  As long as the selector switch is not set to OFF, and the ignition is switched ON, you should have 12 volts on the brn/wht wires at the selector switch and blower switch!

Besides the brn/wht feed wire, the blower switch has a 16-ga tan wire (medium-low speed that runs to the blower resistor), a 16-gauge light-blue wire (medium-high speed that runs to the resistor), and an 18-ga orange wire (high speed that runs to the blower relay and directly energizes the relay, bypassing the blower resistor). 

All fan speeds, except high, are routed through the blower resistor and then on to the blower motor, via a 16-ga dark-blue jumper wire that connects the blower resistor to the blower relay - and powers the blower motor through the blower relay, as long as the relay is not energized.  In other words, by default (on any fan speed except high), the blower relay connects the dark-blue jumper wire and resistor to the 10-ga purple wire running to the blower motor.  Life is good. 

But, because of the nature of the resistor wiring, don't try to puzzle through the 'logic' of the various blower speeds or you'll end up institutionalized.  All of the wires off the blower switch (except orange) will be 'hot' all the time, because of back-feeding through the resistor.   :o   And, life will suddenly seem very bad!   :(

Finally, when the blower switch is set to high speed, the 18-ga orange wire energizes the relay, and the 10-ga purple wire is disconnected from the dark-blue jumper wire and blower resistor, and connected to the 10-ga red wire powered directly off of battery through a fusible link.  The 18-ga black wire connected to the relay is the relay coil ground.

Whew!   :P

Hopefully, this explanation will help you sort out the remainder of your problem.

Yet, I'm surprised at the number of burned connections and components you encountered.  Once you restore proper blower function, you should measure blower motor and compressor clutch current draw - shouldn't be over ~20 amps for the blower and under 3 amps for the compressor.   8)
Rich
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Offline brlarl

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Re: A/C
« Reply #10 on: July 25, 2012, 09:07:30 AM »
I will research based on your info. bd do you by chance have a schematic of the a/c wiring on the 90 Suburban? I believe it's the same as the trucks, everything has been right on where you said it was. Thanks
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Online bd

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Re: A/C
« Reply #11 on: July 25, 2012, 11:51:56 PM »
I will try to dig one up for you, but it will be in pdf format - tomorrow at the earliest.  Good luck with your project.
Rich
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Offline brlarl

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Re: A/C
« Reply #12 on: July 26, 2012, 07:09:37 AM »
Thanks bd!
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Online bd

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Re: A/C
« Reply #13 on: July 26, 2012, 09:13:38 PM »
Here's the diagram in pdf format.  Any luck since your last post?
Rich
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In other words... if people learn by making mistakes, by now I should know just about everything!!!
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Offline brlarl

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Re: A/C
« Reply #14 on: July 26, 2012, 09:27:02 PM »
Thanks BD, no I have not had time to look at it but will do so the weekend.  I'll keep you posted. Thanks Again!!!!
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