A/C blowing fuses

[gchemist]

My truck has started to blow the A/C fuse. Has anyone had this type of trouble? I had to go buy more fuses for troubleshooting. So far, I know it's the compressor wiring. Next, switches and resistor. After that, harness to the switch. I'm just looking for a possible common place of wiring failure. A power wire somewhere is grounding out.

[BigBlocksRule]

You have a homotron in your system.
It's a gay electron that blows fuses.
Get rid if that and you'll be fine.

[pontgta]

I would start by disconecting the compressor, and run the system. I am unsure how well you are with the multimeter, and if you have an amp probe, but should be easy to find.

Start with one wire at a time, verify 12v and ground, and when the system is off check to make sure you do not have a short somewhere.

Which fuse is it ? AC 25 amp?

[gchemist]

It's not the compressor. I pulled the wires off and turnd it on. The fuse blew up right away. If I have the A/C on and plug in a fuse, it will run for a while before blowing. I do have a voltmeter. If I could maintain power, I may be able to find the problem. I'll continue by unplugging pressure sensors, resistor and relay. Electrical troubleshooting is not my thing.

Yea, it's the 25 amp fuse. I can reach under the dash pull and plug in a new one without looking.

[pontgta]

So, i looked at the wiring schematic for my 87, and really this should be easy to trouble shoot. There is really not much that can blow that fuse. My fisrt guess is the blower motor, since you say that it will blow the fuse wioth the compressor wire off.
Turn on the AC with the truck off see how long it runs. If it blows, disconnect the blower motor and see if it blows the fuse again.

All your fan speeds work? Make sure all the the connections are good....i have seen loose grounds cause this issue..

[gchemist]

Thanks for the tips. I'll have to time to look at tomorrow or later this week. I have a truck show on Sat. It sure would be nice to drive it there with A/C. I suspect it's the blower motor. I can't remember if it's been replaced. It does run good. I wonder if the 145 amp alternator after all this time may be causing problems too.

[misternash2]

Originally Posted by BigBlocksRule

You have a homotron in your system.
It's a gay electron that blows fuses.
Get rid if that and you'll be fine.

i just spit coffee on my keyboard.

[misternash2]

let us know what you find. my guess would be to locate all loads on that circuit and unplug them one at a time until your fuse blows. then you'll know you're losing power to ground in between.

[hatzie]

Does the fuse blow with the controls set on vent or heat?

The '83 compressor power feed from the dash controls is light green.
It feeds through the firewall to a two position Packard 56 connector. The light green wire wyes out to the pressure cutout. The return from the pressure switch is dark green on the same connector half.
The mating half of that connector feeds the compressor via a dark green wire and the high idle solenoid on the carb with a light green wire. I'd check the high idle wire for damage and maybe the 30 year old solenoid for high current draw.
After you check there look over both green AC wires for damage.

[hatzie]

This may help...

[gchemist]

Thanks for the diagram. I have an 83 factory manual that I have not referred to. Now a light bulb has gone off!! I didn't install the A/C idle soloniod on the ZZ4. So I wonder, where did I tie off that wire!! I do have an Edelbrock A/C soloniod. I guess I should install it. I'll definately start looking for that power wire!! Thanks for reminding me about it!!

I'll test on the vent and heat positions. The switch will have to be at those positions. Since A/C max is first, once the switch is moved, POP goes the fuse.

[gchemist]

I found the problem today. A large wiring harness routed over the blower motore power wire wiggled it loose. The harness was rerouted and secured. Fan and A/C work fine now. I may need to replace the fan power wire connector. It's fit a little loose due to age. Due to troubleshooting, I drained the battery dead. It will only take a few hours to charge up the red top battery.

[gchemist]

Apperantely, I did not fix the problem. I didn't notice but my alternator was not charging. I drove around two days before noticing power loss. I guess the low voltage kept the fuse from blowing. I replaced a failed switch and the alternator is charging to full power. The fuse is blowing again. It does not blow on vent settings. So yes, I suspect the fan starting up is drawing too many amps. I'm going to pull the fan out and check operation. Due to age, it may be worn out. The system ran fine for the two days when the alternator was not charging. I use a switch with a light to supply 12 volts to the alternator. When the alternator activates to charge, the light turns off. When the alternator is not charging, the light is on. It's a great way to tell me if the belt is off or another problem exists.

[hatzie]

It doesn't blow with the blower running at all 3 speeds in VENT, HEAT, or DEF??

[gchemist]

I have not checked heat or DEF. I'll check this afternoon. Definately not on Vent. As soon as I move from vent to A/C it blows.

[hatzie]

Originally Posted by gchemist

I have not checked heat or DEF. I'll check this afternoon. Definately not on Vent. As soon as I move from vent to A/C it blows.

The fuse blows with the clutch unplugged. So it's not the clutch electromagnet.
If it's not blowing on VENT then it's not likely it's your heater fan.

Test the AC wires for a short or a damaged TVS diode at the compressor connector with a DMM;

• Switch off the ignition.
• Unplug the low pressure cutout switch and tie the the connector up
• Unplug the compressor and tie the connector up as well.
• Switch the dash control to VENT.
• Set your DMM to Resistance.
• Test the Compressor clutch TVS Diode by hooking your meter leads to the compressor connector leads and checking for a short then reversing the leads and looking again. It should show an open circuit in one direction and dead short in the other. If the meter shows a dead short no matter which way you hook up the meter leads the TVS diode is blown.

If the TVS Diode tests OK test the clutch feed wires.

• Hook one lead to a good engine ground close to the low pressure switch connector and verify 0 ohms dead short to the battery negative post.
• Move your DMM lead from the negative battery post to the Dark Green wire terminal in the Low Pressure cutout plug.
• Your DMM should read infinite resistance "0.L" or "1 . ". If the meter reads an actual value you've found your short. If not Start over with the Light Green wire.
• Physically check the offending wire for damage and repair it.

[gchemist]

Thanks for the detailed instructions!! Just what I need! Now, where is the TVS diode located? I can't find a replacement part for it on websites.

[hatzie]

Originally Posted by gchemist

Thanks for the detailed instructions!! Just what I need! Now, where is the TVS diode located? I can't find a replacement part for it on websites.

It should be across the compressor plug. I don't think the TVS diode is a standard replacement part.

[gchemist]

Ya know, I think I remember seeing those now. Well, mine does not have it anymore. It's straight wired. Here is a pic of a what a clogged orifice tube can do to a clutch!!

[gchemist]

Okay, busted out the ohm meter. All the wiring and sensors checkout. I removed the fan. The bearings on the fan are shot. The fan turns but drags. The amount of amps to start the fan kept blowing the fuses. A new fan costs $14.99. I removed the plastic drum and put it on the new fan. Installation was easy. The fuse blew on the first try to crank it up. I ran the fan on vent for a few minutes. The low speed broke in the new bearings and electric motor. After a few minutes, the fan was run at full speed. What a difference!! The new fan spins so fast. I can hear air going through the vents even with the radio on. After breaking in the fan, the A/C settings were tried. No more fuses blowing!! A/C works great again. Now that it spins properly, cooling the cab is fast.

[pontgta]

I am glad you found the problem... Its way toooooo hot with out AC

[hatzie]

Good to hear. Stay cool. Thanks for the AAR.