C10 Issues

[Simple10]

Hey guys. I hope someone can help me out here, I have a C 10 and when I put the fan switch on full the air conditioning works great, when I turn it to medium or low on the switch it still works but you can’t hear the fan and when I give it a boot full of acceleration when driving it feels like I’m running on 7 cylinders .....missing and farting , pig rooting , then I hit the Aircon fan back on high and it drives like a dream. any ideas where to start?
Must be an electrical problem somewhere .

[LockDoc]

Originally Posted by Simple10

Hey guys. I hope someone can help me out here, I have a C 10 and when I put the fan switch on full the air conditioning works great, when I turn it to medium or low on the switch it still works but you can’t hear the fan and when I give it a boot full of acceleration when driving it feels like I’m running on 7 cylinders .....missing and farting , pig rooting , then I hit the Aircon fan back on high and it drives like a dream. any ideas where to start?
Must be an electrical problem somewhere .

Wow! I never heard of that problem before. Must be a short in the wiring somewhere. I will have to think on it..... I have never had a truck with factory A/C. I do know that medium and low speed for the blower go through the heater resistor inside the interior heater box, and the high speed bypasses it. I don't know how the resistor would cause interference with the ignition though. Try unplugging the connector at the A/C compressor and see if it still has the poor running problem with the A/C switch in the medium and low positions.

LockDoc

[maverickmk]

Typically AC/heat blowers are on 2 separate circuits. One for low and medium, then another for high. Look into the low/med circuit, obviously. I am not too familiar with these trucks yet, so I am no help with the actual location of where this circuit is, sorry.
Edit: I just found this thread, maybe it will offer some assistance.

http://67-72chevytrucks.com/vboard/s...d.php?t=216218

[LockDoc]

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Here is a picture of the A/C blower motor resistor location. (#1)

[rpmerf]

Couple thoughts -
Points or HEI?

Do you get the same reaction for low / med / high if the heat is on instead of the AC? If not, follow the AC circuit. I believe some years got something to increase the idle for AC. This may be related.

I am assuming it runs fine with the fan and AC off.

Measure the voltage at the coil with the ignition turned on with the fan in various positions.

Possible ground or short circuit?

[Simple10]

Thanks for the responses I will check out a few things, and another thing I have noticed sometimes when I go to turn the key off if I turn it too far it will like pre-ignite and want to keep going unless I flick the key back to the start then off again ? Again only does this when I have flicked the switch up on the fan too low or medium.... such a pain in the arse....I don’t know why people spend a fortune on doing a car up Then doing a crap electrical job on it .... as Arnold says .... I’ll be back.

[Andy4639]

Check the wires going to the fan switch from fuse block. It sounds like either a wire has melted into another one are they have one jumpered off the ignition wiring some place.

How does it run when no AC at all on?

[Simple10]

Originally Posted by Andy4639

Check the wires going to the fan switch from fuse block. It sounds like either a wire has melted into another one are they have one jumpered off the ignition wiring some place.

How does it run when no AC at all on?

Runs great when air con is on with fan on hi

[franken]

So C10 AC is different than K10?

[Simple10]

Originally Posted by franken

So C10 AC is different than K10?

Couldn’t tell you, this probably isnt original I’d say.

[special-K]

Originally Posted by franken

So C10 AC is different than K10?

Car to elaborate? Offer something helpful? The answer to your question is "no" and now I am pondering why you ask.

To Simple 10 (catchy name), I'm not much on electrical. Especially from afar. What happens when you pull the heat/ air condo fuses? And have you taken a good look up under there at the wiring that is visible?

[Andy4639]

Originally Posted by Simple10

Runs great when air con is on with fan on hi

How does it run when no AC is on? Turn everything off even pull the fuse like Tim suggested.


When the AC is on high it bypasses the resister and has power straight to the blower motor.
Are you sure it's the electrical system???

The levers on the AC control panel also work all the vacuum lines which if not hooked up are have bad section would cause a vacuum leak and the engine would do as your stating. Check all those also.

[rpmerf]

I was thinking about the vacuum lines, but they should not change with fan settings. The vacuum lines are used when the top leaver is set to recirculation. There is one line that opens the door on the passengers side, one that closes the door under the cowl, and one that shuts off coolant flow to the heater core.

[Steeveedee]

You have what appears to be a factory AC/heater box on the firewall. However, the compressor and condenser are aftermarket. This is not a problem, just pointing out what is apparently not original. If the truck runs badly when the fan is running with dropped voltage, I'd suspect that the ignition is improperly tied to the fan circuit somehow. It should be easy to tell. Trace the power wire to the coil back to its source. If the wire goes anywhere but from the coil to the ignition switch, it should be corrected. If any other wires are attached to that wire, then look to see where they go. There are two connections on the ignition switch that get power when the key is on- Ignition, and Accessory. Do you have stock ignition?

As far as over-rotating the key and getting the other problem, this tells me that the above is more than likely the issue, since the engine should quit when the switch is turned to Accessory. The fan, however will run when the key is in the Accessory position. So the Ignition is getting power from somewhere, which would seem to be the blower motor power circuit.