The A/C Amp Thread (1 Viewer)
- Thread starter TrickyT
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
TrickyT
Hate that mud...
- Thread starter
- #122
I just noticed something from the photo you included in post #115. See the position of the red knob on the temperature potentiometer? Compare that to my photo in post #5. Yours is set as low as it can go, which should make the A/C run so much that the evaporator coils freeze over. My guess is that the PO added the black wire because the A/C was not working well and he/she thought the problem had something to do with the board. What's far more likely is that the system is either low on Freon or the expansion valve that sits between the condenser and the evaporator is plugged up. Or maybe there's moisture in the refrigeration circuit. Either way a good A/C shop should be able to diagnose what's wrong. Also, after you remove that extraneous wire you should set the red knob back to something reasonable, say 34° or 35° according to my photo in post #5. You want it set to where the A/C stays on until the evaporator get within 2-4° of freezing, then shuts off the compressor. The adjustable temperature potentiometer is part of the circuit because the thermistor that senses air temperature is not a precise device and the potentiometer allowed the factory to calibrate each sensor. (I have no idea if Toyota actually did such a calibration on every vehicle leaving the factory; I sort of doubt it.) It's interesting to note that in 21st century vehicles like my 2014 FJ Cruiser, the whole A/C system is basically the same as your FJ60. There's still an A/C Amplifier and an evaporator temperature sensor, but of course all the electronics have been updated to modern devices.
Thanks again for all the help. I had noticed my red knob was set wrong based on how you had yours marked. It’s really helpful that you put so much work into it. I rarely have to ask questions on here bc most of it has already been addressed.
83 FJ60: replaced expansion valve, compressor, drier, and evaporator but did not clean out the condensor or lines. Gassed it up with R134 with an AC machine. The compressor would come on for a few seconds and then shut off. Thinking that may be some kind of blockage, and possibly related to an added ground wire to my amplifier, or a bad low pressure switch, I tore it all back apart. This time I cleaned the condenser, evaporator and lines with an ac flush (it said not to do the compressor). I put in a new drier, expansion valve, low pressure switch, and thermistor. Pulled a long vaccuum, then gassed with 0.72kg of R134 with an AC machine. Now I’m getting a short cycle. With it hooked up to the machine the pressure would go to about 30psi and then drop to 10 and it would shut off. It did this several times whether I bypassed the amplifier or not. Does anyone have any ideas? I don’t know if the low pressure switch is shutting it off bc the pressure is dropping but if so, why would the pressure drop? The only other thing I could think of is I have somehow burned up this compressor, but I’m not sure what that would look like? I have another new one I could install but I don’t want to ruin two of them if there is something else I’m missing
TrickyT
Hate that mud...
- Thread starter
- #125
Wow. What a heroic effort! The low pressure switch should open if the output side of the compressor drops below ~30psi. So if yours is dropping to 10, that's why the compressor clutch disengages. So I think your pressure switch is working the way it should. So why can't the compressor make more pressure? You sure you don't have a leak somewhere in the system?
I don't have the FSM for the FJ60, but for the FJ62 it says it takes 800-900g (1.8-2.0lb) of refrigerant. So you may be underfilling the system. Since you've replaced pretty much every component that's about all I can think of.
I don't have the FSM for the FJ60, but for the FJ62 it says it takes 800-900g (1.8-2.0lb) of refrigerant. So you may be underfilling the system. Since you've replaced pretty much every component that's about all I can think of.
Thanks for the response! I’ve tried to do everything correctly bc I really don’t know much about it. There is a sticker on the radiator support that says 0.6 - 0.8 kg R12. From what I have read you should reduce that to 90% which is 0.72 kg so that’s why I’m using that amount. And the machine I am using can be set to kg so that seemed like the easiest way to not make a mistake. But it may be under filled. I could try putting 0.8 and see if it changes.
It passes a “leak test” on the machine, I don’t think it’s fool proof, but I did recapture the refrigerant after it didn’t work and it hadn’t lost any in that amount of time. So I think it’s holding enough to work for a little while at least.
So based on your response my compressor isn’t making enough pressure so maybe the compressor is bad? Maybe it got trash in it from the first attempt or maybe two many cycles has messed it up? I think I saw one post where someone ruined one pretty quick. I have another one but I hate to ruin it if something else is wrong. I found a post where someone had at least one and maybe two bad expansion valves that were new. I hope it’s not that bc it sucks getting it out. But I’m not even sure what that valve does and if it could cause this problem? And just to be clear, the line from the condensor connects to the “IN” side of the drier, right?
Last edited:
Did you pressure / vacuum tested the system? Does it hold pressure / vacuum?
When it runs what are your manifold pressures (high&low) before and after it shuts off?
Low vacuum would say your TXV is not opening and starving the compressor of refrigerant. High pressure indicates possible contaminants in system creating high head pressure on compressor.
Is the electrical AC circuit solid? Check for loose wiring and relays..
also check for air flow at the evaporator and condenser....
With the vehicle off by pass the circuit and feed the clutch 12vdc.. see if it engages and stays engaged without issue...
The txv is what controls his much refrigerant goes to the evaporator and is also the point where refrigerant goes from high pressure to low pressure and from liquid to gas refrigerant... what opens and closes the txv is the bulb that is attached to it via a thin tube..
When it runs what are your manifold pressures (high&low) before and after it shuts off?
Low vacuum would say your TXV is not opening and starving the compressor of refrigerant. High pressure indicates possible contaminants in system creating high head pressure on compressor.
Is the electrical AC circuit solid? Check for loose wiring and relays..
also check for air flow at the evaporator and condenser....
With the vehicle off by pass the circuit and feed the clutch 12vdc.. see if it engages and stays engaged without issue...
The txv is what controls his much refrigerant goes to the evaporator and is also the point where refrigerant goes from high pressure to low pressure and from liquid to gas refrigerant... what opens and closes the txv is the bulb that is attached to it via a thin tube..
Last edited:
Thanks for the info!
I did vacuum test it and it did hold and pass that test.
Low side was going from 10-30 and l believe high side was around 100.
The cycling seemed to be speeding up (every 1-2 seconds) and I got worried it was gonna burn up the compressor so I cut it off.
I have the condensor line connected to the drier IN, is that definitely correct?
I believe the wiring is pretty solid.
The vents are blowing good in the cab.
What’s the chance that the txv is bad?
Would giving 12V to clutch risk burning it up if the txv isn’t working right?
Any other suggestions?
Ideally you wan to power the clutch without the engine running to see if it stays engaged, futhermore with the engine not running you will be able to hear if the clutch stays engaged and or if disengages with constant 12vdc.
I would also check continuity between your dash button and plug at the compressor check both power and ground... and when you do check wiggle them wires to see if continuity disrupts it shouldn't.
Your low side pressures will tell yah if your txv is working as design...
I want to say on 75F ambient temps you want to see 30 to 45 PSIG on the low sides. anything below that is starving for refrigerant...
On the high side 150 to 170psig is what you want to have..
My experiece with short cycling has been with low charge, no air flow on the evap, or condensables on the charge.
Your short cycling is much to quick to call it a short cycle.
Short cycle usually happens in minutes and not in seconds.......
I would let the system run and see what it does...but before you do that... be sure that your compressor has the right amount of oil (usually poe oil for a R134A refrigerant) and if you put it new did it come preloaded with oil ? (they usually do) but i have to ask....
Running the system with low refrigerant wont kill it as long as there is oil in the system and I believe you LP solenoid / switch is doing its job.
An over filled system will damage your compressor as it my flood the compressor.... compressor can't compress liquid....
Also when you installed the new TXV the bulb that controls the it should be placed horizontally against the copper tubing that is coming out of the evaporator and covered with insulating foam tape to give the txv the most accurate readings.
Lastly check the controls on the dashboard for anything that might look out of place make sure your heater valve is shutting off 100% hot coolant tot he heater core.......
Good luck !!
TrickyT
Hate that mud...
- Thread starter
- #130
Let's make sure that it's the pressure switch that is causing the compressor to cycle, because cycling every 1-2 secs is awfully fast. Do you have any test leads available? Something like this would be ideal:
Or a wire with a small alligator clip on the end:
Attach this to the same place on the relay on the A/C amplifier where the black wire you previously had used to attached. (It would be best not to solder a wire on -- this is only for a test.) Attach the other end to a convenient ground point. Start the engine and turn on the dash A/C switch. The compressor should engage right away and stay engaged. It should be just fine to leave the compressor on for a minute or so. If the compressor is not cycling then there's something funky going on with the A/C amplifier. If it does cycle then it can only be due to one of four things: the pressure switch, a bad relay on the A/C amp board, a bad compressor clutch, or bad wiring somewhere in between.
Or a wire with a small alligator clip on the end:
Attach this to the same place on the relay on the A/C amplifier where the black wire you previously had used to attached. (It would be best not to solder a wire on -- this is only for a test.) Attach the other end to a convenient ground point. Start the engine and turn on the dash A/C switch. The compressor should engage right away and stay engaged. It should be just fine to leave the compressor on for a minute or so. If the compressor is not cycling then there's something funky going on with the A/C amplifier. If it does cycle then it can only be due to one of four things: the pressure switch, a bad relay on the A/C amp board, a bad compressor clutch, or bad wiring somewhere in between.
@TrickyT @MANUCHAO thank you both for the help. I’ve now got some new things to try.
Could one of you confirm that the line from the condensor goes to the IN side of the drier?
Also, I’ve been reducing the r12 amount by 10% but I found one thread where someone had went through a lot of this and found that it ran better on r134 without being reduced. A few people on here have said this could be a symptom of low refrigerant so I’m going to try that first and see if maybe it was just that all along. At least that seems like an easy thing to try.
Could one of you confirm that the line from the condensor goes to the IN side of the drier?
Also, I’ve been reducing the r12 amount by 10% but I found one thread where someone had went through a lot of this and found that it ran better on r134 without being reduced. A few people on here have said this could be a symptom of low refrigerant so I’m going to try that first and see if maybe it was just that all along. At least that seems like an easy thing to try.
TrickyT
Hate that mud...
- Thread starter
- #133
Also, In one of your earlier posts you said "the pressure would go to about 30psi and then drop to 10psi" which I assumed, now I think mistakenly, was being measured on the output side of the compressor. But then in a later post you said "Low side was going from 10-30 and l believe high side was around 100." So my previous comment in post #125 about the compressor not making enough pressure should perhaps be disregarded. In my FJ62 FSM it says that in a normally functioning system the low side of the compressor should read 21-28psi and the high side should read 206-213psi. (Conditions: air temperature 86-95°F, engine @ 2000rpm, blower fan set to high speed, temperature control set to cool.) So the 100psi you are measuring is too low, which may be attributable to not enough freon.
You can temporarily bypass *all* of the A/C control logic by disconnecting the connector on compressor clutch and running a wire directly from the clutch to +12v on the battery. The clutch should then engage continuously and allow you to measure input and output pressures of the compressor and compare the results to the numbers above.
Lastly, you may be dealing with more than one problem, which make diagnosis more difficult. I now think you should bypass the A/C control logic altogether, as I describe in the previous paragraph, and just make sure the refrigerant circuit is working correctly. Once you confirm that the mechanical/freon half of the system is working you can move on to the control logic. In other words, divide and conquer.
You can temporarily bypass *all* of the A/C control logic by disconnecting the connector on compressor clutch and running a wire directly from the clutch to +12v on the battery. The clutch should then engage continuously and allow you to measure input and output pressures of the compressor and compare the results to the numbers above.
Lastly, you may be dealing with more than one problem, which make diagnosis more difficult. I now think you should bypass the A/C control logic altogether, as I describe in the previous paragraph, and just make sure the refrigerant circuit is working correctly. Once you confirm that the mechanical/freon half of the system is working you can move on to the control logic. In other words, divide and conquer.
Man thanks again, I think you’re right that there could be more than one problem. A lot of things have pointed to not enough refrigerant. So I’m definitely going to add a little more and then connect 12V directly and see what happens. Hopefully I can do this tomorrow.
So we hooked it back up and this time he put 0.9kg (2 pounds) which is more than I was planning on... but with the 12V directly to the compressor it came on and stayed on and started cooling which is much better than it had been doing. Low pressure side would start around 40 and gradually (less than a minute) drop to zero. High side was around 180. So then we hooked it back up to the regular wire and basically the same thing happened but as the Low side would get to about 10 the compressor would kick off which made sense that the low pressure switch was working. The low side would build back up and it would kick on and repeat itself. Which seemed ok but it was probably cycling too fast (around 1 minute). It did this a few times but each time the high side would get a little higher and after 3-4 cycles the low side got to zero and the compressor didn't kick off. It even went into a vacuum and didn't kick off. The high side got to about 320. So now I am wondering if the low pressure switch has somehow quit working (it's a brand new toyota switch)? And even when it was working (and even when directly given 12V) what would cause the low side to drop so quickly? Could we be overfilled, still underfilled? The only thing I haven't replaced is the condenser bc they aren't available and there doesn't seem to be a clear alternative. If anyone knows of a different condenser that works, please let me know. But I did run cleaner and air through this one and it didn't seem to have blockage. There were still some bubbles in the sight glass on the drier.
TrickyT
Hate that mud...
- Thread starter
- #136
Someone please correct me if I'm wrong, but I believe the "low pressure" switch connects to the high pressure side of the system. It's there so that if there's too little freon in the system or the compressor isn't working correctly, it stops the clutch from engaging and potentially destroying the compressor. So it's just a safety switch. It's the A/C amplifier and the thermistor that controls the normal cycling of the compressor. You don't want moisture freezing on the evaporator coils and blocking air flow, so the A/C monitors the coil temperature and cycles the compressor off a few degrees above freezing. Then, because the fan is blowing air over the evaporator, it warms up and the compressor comes back on. A one minute cycle time seems OK to me, but it depends on the ambient air temperature and how well the overall system is working. But you do want to make sure the red potentiometer on the A/C amplifier is set to cycle off the compressor before the evaporator coils start to freeze.
However, 320psi is much higher than the 206-213psi specified in the FSM. And I wouldn't expect the low side to drop all the way to 0psi. The FSM says if the low side pressure drops to 0 that the expansion valve may be clogged.
However, 320psi is much higher than the 206-213psi specified in the FSM. And I wouldn't expect the low side to drop all the way to 0psi. The FSM says if the low side pressure drops to 0 that the expansion valve may be clogged.
That makes a lot of sense. You're right, the pressure switch does attach to the small high pressure line. It is a brand new expansion valve but it could be clogged. Of course it's the hardest thing to replace. It isn't denso, so I will order a denso one and make sure it's the best chance to be good before I tear that out again. Thanks again!
TrickyT
Hate that mud...
- Thread starter
- #138
The expansion valve includes a "bulb" that controls the opening of the valve. I don't know how to test if the bulb and valve are working correctly as a unit and the FJ62 FSM is silent on this issue except to acknowledge the bulb's presence. But if the expansion valve was "closed too far" (whatever that means) then the pressure on the low side of the system could go to zero. I think that how this part of the A/C system works would be basic knowledge for any competent A/C technician. When I started this thread it was all about the A/C amplifier circuitry, so I think I can't really help your specific issue much more than I already have. But do let us all know how problem get resolved.
