joshik

a while back i posted regarding my ac fuse blowing.

well i did some trouble shooting today after work. accessed the secret spot for the ac fuse behind the glove. i took out the blown fuse and jumped it with some wire. i turned on my motor and turn on the fan, and hit the ac button. motor reved up and held. i turned it off. i was scared that i might blow something else. so i had someone hit the ac button as i layed underneath and watched the compressor. i dont know much about ac and compressors but i watched the compressor. when the ac was engaged, the "wheel" (im assuming the clutch) that is attached to the wheel with the belt started to try to spin. it would do a quarter turn, stop, small turn, etc. seemed like it wasnt engaging all the way. it would make a scratching noise too. so im guessing that the clutch isnt engaging therefore not turning the compressor. does that sound about right? could it be just too dirty? it has a lot of dirt on it. also i noticed that when the ac switch was engaged, the wheel with the belt would move forward slightly. is that normal?

im going to call toyota and then my local discount parts store to see how much a new compressor would cost.


anyways, any help would be greatly appreciated!

AaronW

Joshik,
I hope someone replies to your post because I'm having the same trouble. I've checked my r-12 level and it is good. I bypassed the low pressure switch, and it is good. I am now checking the ac dash switch. BTW, Roger Brown is a great guy. He replied to my email asap.

Have you checked the gas level in your ac system?
Have you bypassed the low pressure switch to determine if it is bad?
Have you checked your ac dash switch?

Hope you find the problem soon and post up the fix.

joshik

well, i didnt really get to try checking the gas in my ac system or bypassing the low pressure switch. i jumped the ac fuse with a piece of wire and started up the ac. it started to go and the motor reved up a lil. would any of those other tests have anything to do with the clutch not engaging/spinning properly? im not sure how ac systems work in the first place but it seems that the clutch, or that wheel infront of the compressor pulley is supposed to turn when the ac is turned on. am i correct?

BC Rider

joshik:

I could not find part 1 of this thread so some of this information you may have already. I had a similar problem in my 1990 truck some time ago. The minute I pushed the AC switch the fuse would go. Just got a brief flash of the green indicator and then nothing.

In my case it turned out to be the insulation for the wires to the compressor clutch switch had become brittle and had flaked away allowing it to short. I ended up smearing them with some of the liquid insulator as they were a PIA to get at. It's held up for more than 2 years, but I will one day change them out.


While I was trying to figure this out I gathered some other info which may be of some use to you. I ended up with the following "do list" but stopped checking once I found my problem.

1. Check resistance at clutch connector - should be 3.5 to 5 ohms

2. unplug ac mag clutch coils and try switch

If above does not solve then......

3. check clutch relay?

4. Check the ac eco - toyota calls it an "amplifier"

I'm pasting in some posts from various places I copied at the time. Just understand I can't vouch for their accuracy as my problem turned out to be simple so I cut the do list short:

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I would certainly try to feed 12v direct to the clutch connector with engine turned off. YOu would hear it click on and off. If it does not, then you have the culprit. IN fact, instead, you can use a multimeter just to check continuity at the clutch connector: this normally draws half an amp or so, so it might read 15 to 30 ohms...+/- a few ohms; anyway, if open (damaged) , it will read in the hundred thousands ohms, accounting for any dirt that might provide a residual path for current.

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Those Bewildering Toyota A/C Controls
Motor Service, July, 2000 by Phil Fournier
Save a personal copy of this article and quickly find it again with Furl.net. Get started now. (It's free.)How many of us have felt we had a pretty good grasp on electronics until we tried to troubleshoot a "simple" air conditioning problem on a Toyota? We spent hours staring at the wiring diagram, often unable even to figure out which wires should be power and which should be ground. If we don't happen to have a factory manual or an after-market source that uses factory diagrams, we're faced with several mystery boxes called "amplifiers" with numerous wires connected to an unmarked box. On top of these problems, the vehicle seems to have been a dumping ground for someone's excess supply of relays. So, we're going to concentrate on identifying the operation of the mysterious component known as the "A/C amplifier," and its influence on the control of the compressor clutch circuit.

Simply knowing that the amplifier's job is to pull pin 6 (pin 11 on some models) to ground (around 400 mV) in order to energize the magnetic clutch relay is a huge help. This is located in the relay box next to the battery and is usually the one closest to the front. Once pin 6 goes to ground, pin 2 of the relay should have power going out of it, which will branch off to both the A/C compressor clutch and the A/C fan relay #3. However, the idiosyncrasies of this system lie in the number of inputs required to insure that the amplifier maintains a ground on pin 6.

Many techs are confused when they notice that the amplifier has wires going into it from the ignition coil, the "revolution sensor", and a thermistor. We could think of the ignition coil and revolution sensor inputs as clutch protection devices. The thermistor is simply an evaporator temperature sensor that signals the amplifier to cycle the compressor when the evaporator gets too cold. This signal comes in on pin 3 and the thermistor can be checked between pins 3 and 9 (ground inside amplifier) for a resistance above 1000 ohms. The thermistor is the negative coefficient type, so cooler temperatures will cause resistance to be higher. Pin 8 of the amplifier is a standard coil negative tach signal, while pin 13 should be an AC sine wave whenever the compressor is turning. When it gets a power signal in on pin 1 from the A/C control button, the amplifier pulls pin 6 to ground for five seconds, while watching for an input on pin 13.

Here's the trick: If it sees no corresponding signal on pin 13, IT WILL LET GO OF THE GROUND ON PIN 6. Now, consider how many things may cause that: a bad revolution sensor in the compressor, a faulty magnetic clutch relay, a slipping compressor clutch, a broken drive belt, and any number of wiring problems.

Note also that the system has to have a small charge of refrigerant in it to close the dual-pressure switch, which is inconveniently located underneath the battery tray. The dual-pressure switch is so called because it opens at under 30 psi and opens again at over 384 psi. An easy place to test for a sufficient refrigerant charge and a good dual pressure switch is at the idle-up solenoid located in plain sight on the right side of the firewall.

Power from the 10 amp A/C fuse (located in a fuse box behind the right kick panel) flows to the A/C control switch and also to the dual-pressure switch. If it makes it through the pressure switch it goes on to four other places: the magnetic clutch relay the idle-up solenoid, pin 2 of the A/C amp

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