1999 Tacoma 2WD 3.4L A/T

Hello everyone

I've been talking to some guys on another forum reference a problem I'm having with a constant blown AC fuse and thought I'd reach out to another forum for some additional guidance. Not to say the guys on the other forum aren't helpful but looking for other ideas.

So here is my problem:

The 10A AC fuse blows every time I push the AC button and activate the blower fan. Don't have any history on the truck, but the AC has never worked, meaning the clutch never engaged. Until now, I decided to look into it.

Believing the switch maybe bad, I replaced it with a cheap internet find. Still blows fuse.

I unplugged compressor plug. AC fuse still blows when button pushed.

I borrowed a friend's cheap short finder and observed the following:

1.) When the AC switch is off or taken out of the dash, I have a tone on my receiver from the short finder from the fuse to the switch and from the fuse to the compressor plug. When I press the AC button, the tone goes away.

Here are some other observations:

1.) Compressor clutch engages momentarily when I jump from +battery to compressor
2.) With the AC fuse out, I tested the terminals. I have GND continuity on the right terminal, but nothing on the left. I don't know if that means anything or not. I removed the headllight fuse and did the same test and saw that there was GND continuity on both terminals. I made a video to show everyone.


I'm not sure what I need to check next. I assume it's a short. I think it's odd I lose continuity with the short finder when the AC switch is pressed. I thought it should be the opposite. Could the new switch be bad? THought about buying an OEM one in case I got some crossed cheapy from China...

thanks

 

First, yes, I would definitely replace the switch with an OEM one. Not necessarily because it might be the problem, but just because it's always best to go with OEM. Just my opinion, though. Always go with OEM for ANY part, whenever possible.

If I had to bet on what could be causing the AC fuse to blow, I would bet on the AC Amplifier. They have been known to fail.
Then, check the Heater Control Relay, and the wiring to/from it.
The next thing I would check is the blower motor, and then the blower switch. Then, check the wiring for the AC Amplifier, the blower motor, and so forth.
You're loosing the ground continuity due to the Dual Pressure Switch being open due to low pressure in the AC system, read through the AC Amplifier. The other side won't read continuity to ground as there are components in the circuit. The blower motor, and the blower motor switch. Obviously, to activate the AC, you need the blower motor switch in something other than OFF.
Does the blower function correctly in Heater mode? Even just in the fresh air setting. In other words, anything other than AC? If so, you've eliminated those two components, and the associated wiring from consideration.
Always examine any wiring involved with the system whenever it passes anywhere near a possible abrasion point. IOW: where the wire could possibly be rubbing against anything. An abraded wire that touches metal could well be the problem with the AC fuse blowing.

Good luck to you. Chasing abraded wires can be a real joy </end sarcasm>.
Pat☺

 

I appreciate the response.

So I did a few other things. With the AMPLIFIER unplugged, it still blows. I also unplugged the defroster plug ( controller knobs - no stand alone defrost button) and it still blows.

The blower works fine. It blows in heater mode.

I'm not sure what the heater control relay is or where to find it. All wires looks pretty damn good with no obvious burn marks, etc. I don't know how I'm to visualize everything since most is hidden up in the dash with a protective sleeve.

 

Now you know why I said that chasing wires can be so much of a PITA.

It's in the same fuse/relay box the AC fuse is located in. Here's a picture of it:


Hope that helps.

Given the length of the cable run, from the relay box, (RB), there's lots of possible abrasion points between the RB and the rest of the AC system. Anywhere it turns a corner, goes through the firewall, etc.

You might take a look at the AC magnetic clutch. Should be right on top of the compresor. Not easy to find from above. Also, once again, given it's location, you might want to look at it's wiring. That looks like a place with a lot of moving parts that can abrade wiring.

Check ANYthing that has to do with the AC. There's a switch right behind the glove box, the magnetic clutch, and so forth.


I've attached a PDF with parts locations shown. It should be helpful, I hope. Again, if it has to do with the AC, check it carefully. If it's a switch, or relay, ohm it carefully, to be sure there's no path to ground. Again, check any wiring for wear/abrasion. Lots of wire runs, lots of possibilities. Unplug anything that has to do with the AC, and se if it still blows. You're gonna need more than a few fuses

Hope something helps...
Pat☺
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