A/C Amp or Control Unit (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Mar 17, 2008
Threads
42
Messages
206
Location
Columbus, OH
Good Morning everyone, hopefully I didn't miss a thread about this in my search.

I currently do not have A/C in my recently acquired 40th and would like to hopefully rectify the issue before the weather gets too warm. Symptoms are the engine idles up as I feel like it should when I push the A/C button but the compressor does not actually engage and nothing more than lukewam air comes out of the vents (low 50s ambient) I tried all functions to see if I could trick it into working (defrost/recirc/auto, etc) but nothing seemed to work. All blower functions and temp control seem to work OK.


Backstory is...The truck was purchased from a family member who states he had it inspected by two different shops that claim it is the control unit (found one invoice confirming this) and that the rest of the system is in great shape. I'm trying to figure out if this seems like an actual control unit failure or if I should be investigating the amplifier that I read about failing on these Auto units. I read that the amp can get corroded and fail but I didn't find a definitive location as to where this is (I read by the pedals and also behind the glovebox?) Also read that it might be possible to clean it to restore its function?

I'm just trying to find the best avenue to pursue since both options seem to be very pricey with replacements.

Appreciate the help, feel free to ask for clarification if something I said doesn't make sense.
 
Get the correct electrical wiring diagram and troubleshoot the relevant parts before investing in an auto AC amp.

There are numerous things that could be preventing the compressor clutch engaging.
 
Get the correct electrical wiring diagram and troubleshoot the relevant parts before investing in an auto AC amp.

There are numerous things that could be preventing the compressor clutch engaging.

I'm personally terrible with electrical components, including wiring diagrams, not to mention I have no tools to do any electrical testing (many special tools were stolen from a storage unit a few years ago). I still haven't been able to find a clear diagram as to where these parts might be or what components it could even be. I'm just trying to do some basic troubleshooting with the information I was given from the prior shops (that it is the unit).

Edit: At this point I'm really just trying to determine what it might be given those symptoms and diagnosis so I can look into getting those tested.
 
Last edited:
I'm personally terrible with electrical components, including wiring diagrams, not to mention I have no tools to do any electrical testing (many special tools were stolen from a storage unit a few years ago). I still haven't been able to find a clear diagram as to where these parts might be or what components it could even be. I'm just trying to do some basic troubleshooting with the information I was given from the prior shops (that it is the unit).

Edit: At this point I'm really just trying to determine what it might be given those symptoms and diagnosis so I can look into getting those tested.

Then you probably need to find someone with the tools and expertise to deal with this job. If you find a really cheap auto AC amp throw it in.. it's very easy to change.. but if something else is messed up that caused the Amp to burn up you'll just ruin that one too.

Granted.. it's not unheard of for just the amp go out, IIRC.

There are three separate relays and a water temp switch that can all keep the clutch from engaging even if the Amplifier is telling it to, for a small example of the number of possibilities.
 
If the idle is changing it isn't the AC amp. When that is unplugged, the AC light might come on for the dash, but nothing changes.
 
I'm going to say you don't have enough system pressure. If you don't have enough refrigerant or if you have too much the AC compressor won't turn on. So, I'd take it somewhere that services AC and ask them to check it out for you.
 
You need a multimeter and a wiring diagram and then you need to start troubleshooting. Otherwise you are just making wild guesses as to what might be wrong, and that approach can get expensive quickly as you replace good parts based only on hunches. If you're not good with electrical stuff, then find a friend who can help.
 
Last edited:
you probably read one of my old threads. it doesnt sound like its one of the amps. to answer your question, yes there is an amp behind the glovebox AND one to the right of your right knee. behind the stereo and to the left. that is the one that fails because of water getting in there but im nearly certain yours is fine if everything else is functioning. also note that the compressor is always "ON" and its the electric clutch that receives the signal from the control unit, via a relay no doubt, to engage. there arent a lot of things to prevent the clutch from engaging. there are a couple very easy tests to see if its the clutch. yes system pressure is one of them. the plug that needs to be jumped is near the sightglass that is to the right of the battery. follow the silver pressure lines. 4 pin plug with maybe only 3 wires in it. look for the EWD so you can at least locate these parts.
 
Today while messing around with it after work the idling up seemed to stop after pushing a few buttons and then hitting the A/C button, was a brief moment with no response from the unit itself too. I might call the shop it was inspected at and see if he may remember what all he checked; the invoice says "Compressor was not running and was not getting power. Traced a/c electrical and found a bad control head"

Why does and electrical issue seem more daunting than a complex mechanical issue to me?!

Glad to know you guys don't seem to think it sounds like an amp problem.
 
Why does and electrical issue seem more daunting than a complex mechanical issue to me?!

Because you don't have experience.

Anyone doing driveline work can do electrical once they have learned the tricks.. but yes wiring diagrams are daunting until you learn how to read them.

You need to get a wiring diagram for an anniversary edition. I have the one for a lexus with auto AC and it is VERY different from a 96 cruiser.. the difference between one relay to worry about and three.

One good sign, IF you are right about the raised idle.. on 96 and 97 LX450s with auto AC the "idle up" signal to the ECM comes from the amplifier, and is basically just a branch off the circuit to the compressor clutch, AFTER all of the relays and complication.

Meaning the signal to the clutch is apparently getting pretty far.. just not all the way. The little blocks with letters and numbers are individual connectors, and the number beside it is the pin #. Between the I14 splice to the ECM and the compressor clutch is connector EA1, which is under the fuse block (one of three in that location), and ED1 is the small connector under the air cleaner. I'd check at both of those locations whether you are getting +12v. ED1 is easier, as it can be disconnected and the engine still run. EA1 will be tricky, as a TON of wires go through there and the engine may not run without it. And there are rubber gaskets on each pin so you can't just get at the wire from the back of the connector like you can the ones inside the cab.

I'm attaching the relevant page from the EWD for a 97 LX with the auto AC. Yours is likely similar, though you NEED to find a correct wiring diagram to find out for sure. There are often wire color differences between LC and LX.


97LXAC.jpg



Get a decent multimeter and watch some youtube videos. I'd bet you can figure this out.
 
Well I did some more digging around today, found the temp sensor in the unit disconnected from it's spot and just laying in the dash...also discovered that at times the compressor is trying to engage and the front of it looks like this when doing so...it just kinda flaps like this as it tries to spin. Yes I made a rookie mistake and recorded in portrait. :bang:

 
Well I did some more digging around today, found the temp sensor in the unit disconnected from it's spot and just laying in the dash...also discovered that at times the compressor is trying to engage and the front of it looks like this when doing so...it just kinda flaps like this as it tries to spin. Yes I made a rookie mistake and recorded in portrait. :bang:



That is more-or-less how the compressor clutch works, only it's not supposed to move nearly that far. Should be less than 1/16".

What is supposed to happen is the electromagnet mounted on the compressor nose behind the pulley "pulls" that clutch plate mounted to the compressor shaft into the pulley, and the friction between the pulley and that clutch plate is what makes the compressor shaft turn.
 
The "fix" for my old 450 was pulling the HVAC unit & flipping the dip switch on back to make it run like a standard unit for a Toyota.

Hated that auto climate control logic, either it was smarter than me or I wanted to dehumidify running the AC with the heater cranked out the defrost vents & it didn't want any part of it - either way, if you want to simplify you pull & flip the switch.
 
That is more-or-less how the compressor clutch works, only it's not supposed to move nearly that far. Should be less than 1/16".

What is supposed to happen is the electromagnet mounted on the compressor nose behind the pulley "pulls" that clutch plate mounted to the compressor shaft into the pulley, and the friction between the pulley and that clutch plate is what makes the compressor shaft turn.

Yeah more or less I can understand how that clutch works, just have never seen one with that much play in one section only, It only rocks in that one direction. Guess this just makes it all more interesting.

Also, CEL came on and drivers door lock started to get slow today (3 of 4 doors now)! :crybaby: The joys of a 20 year old truck.
 
The "fix" for my old 450 was pulling the HVAC unit & flipping the dip switch on back to make it run like a standard unit for a Toyota.

Hated that auto climate control logic, either it was smarter than me or I wanted to dehumidify running the AC with the heater cranked out the defrost vents & it didn't want any part of it - either way, if you want to simplify you pull & flip the switch.
I don't like it either. Are there threads that document this process?
 
It's a pretty simple process: remove the lower panel and unplug the climate control unit to pull it out. The FSM has instructions on how to remove the lower panel, if it's not obvious.

You'll have to pull the gear selector into low to get the panel out.
 

Users who are viewing this thread

Back
Top Bottom