I have a '95 Tercel with a retrofit AC. This summer the A/C simply stopped working. Taking it to the Toyota dealer, I was told that the A/C needs to be evacuated and recharged and that it would work out to around $170. Now, after this was done, I was told that the A/C was atill not working as it needed the amplifier to be replaced and that they could not give me a qoute on it as their parts shop had no power. We had a thunderstorm at that time and they had a pwoer failure. At that point I thought the amplifier was a small part so I didn't create any fuss. Later, calling them I found out that the amplifier is another $300 or so. Now, my question is, should they have been able to figure out during the problem diagnostic itself that the amplifier needed to be replaced or is it something that they could not tell without evacuating and recharging the A/C?
I have a '95 Tercel with a retrofit A/C. This summer the A/C simply stopped working. Taking it to the Toyota dealer, I was told that the A/C needs to be evacuated and recharged and that it would work out to around $170. Now, after this was done, I was told that the A/C was still not working as it needed the amplifier to be replaced and that they could not give me a quote on it as their parts shop had no power. We had a thunderstorm at that time and they had no power. At that point I thought the amplifier was a small part so I didn't create any fuss. Later, calling them I found out that the amplifier is another $300 or so. Now, my question is, should they have been able to figure out during the problem diagnostic itself that the amplifier needed to be replaced or is it something that they could not tell without evacuating and recharging the A/C?
You say it simply stopped working. Does that mean no air circulation within the car or just warm air circulation? Can you look under the hood and see if the compressor clutch is engaging? What is an "amplifier" for an AC system?
"Amplifier"? That is a new one on me. I think they are taking you to the cleaners. I am not sure what they are calling a amplifier. A/C system are pretty simply really, a compressor to compress freon, a condensor to cool the hot compressed gas and convert it back to a liquid, a expandtion valve that expands the compressed cooled liquid to a gass again and a evaporators the the gas expands and cools in which cools the air you get in the car and then it is back to the compressor to start all over again. Basically most of the time it quits cooling it is from lack of freon or defective pressure switches or controls that prevent compressor from running. SOme time it can be from a clogged expansion valve too but the point I am making it that it is a pretty simple concept in theory and it is not hard to find out what is wrong with proper test equipment. My advise is to get you money back if you can (because they told you the first time that it would be fixed) and go somewhere else because they are not being straight with you.
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 amplifier, and also to the A/C cut amplifier.
I wish I could tell you that the pin numbers on all years and models of cars duplicate the pin numbers I gave above. Unfortunately, this is not the case and you'll need the wiring diagram specific to the year and model you're working on. Also note that though all systems have an A/C amplifier very similar to the unit I describe above, models with push-button controls should be considered Auto Climate Control and are equipped with a couple of extra mystery boxes that complicate diagnosis even more.
The moral of the story is this: Make sure your service writer understands how difficult it may be to troubleshoot a simple customer complaint of "A/C doesn't cool." Verify the easy stuff first, such as checking for power at the idle-up VSV (vacuum switching valve). If you don't find the problem quickly don't be afraid to charge top dollar for your diagnostic time. Rest assured that the mass merchandiser down the street isn't going to take the job away from you if you quote too high.
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Yes, Toyota AC's have an amplifier, probably located under or behind the glove box on your car. It controls the operation of the AC and $300 sounds about right for the part. The amplifier makes sure that the engine is running when engaging the compressor clutch; it compares engine and compressor RPM and disengages the compressor clutch if there is too big a difference in speed; and through control of the clutch engagement, it controls temperature to a certain extent.
Like Hachiroku mentioned, you need to have the system properly charged to check the amplifier operation because without coolant, the compressor will not engage. Amplifiers are pretty reliable and do not fail too often. When you mentioned that the AC was retrofitted, was a genuine AC kit installed or an aftermarket kit? The dealer should check the connections to the amplifier before changing it - or, you want to make sure that you will not be charged for the part if the original one was not the root cause.
Go read Hachiroku's 114-line response, but the short answer is no, they needed to evacuate and recharge the system (problem #1) before they could find the bad AC Amplifier (problem #2).
You can call any wrecking yard and pick up a good used one for a lot less than $300. If the wrecking yard knows what they're worth new, they could charge as much as $150 - and this is taken off a car that they bought for as little as the $200 scrap value of the steel.
Is that a great racket to be in, or what? ;-)
The AC Amplifier has several important functions that Hachi spells out for you in all the gory details. But in plain english... ;-P
The AC Amplifier has two main jobs - first, it monitors that the AC compressor is turning at the same speed as the engine is running, and cuts it off if it senses there is a problem - if the compressor has mechanical problems and starts jamming or locks up solid, the fan belt driving it will soon burn up and break, disabling the car. This is bad. And if the compressor clutch is slipping from wear or compressor trouble, the friction will catch the clutch on fire - this is worse.
In either case, it's much better that the AC Amplifier sense the compressor problem, cut off the clutch power, and flash the AC button indicator light as a trouble indicator.
And the second main job of the AC Amplifier is to monitor the evaporator coil temperature under the dashboard with the thermistor sensor, so the coil can't ice up solid with condensed water and stop working. It cycles the compressor on and off so the core has a chance to defrost every few minutes.
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