A/C Compressor clutch not engaging, possible A/C Amplifier malfunction

[tye-bo]

Hello all,

I have done searching for A/C related problems and have found most of them have been posted here (although none of them pertain to my situation), so, hopefully this is the right section for this thread.

I’m currently diagnosing why my A/C compressor clutch won’t engage, and I have narrowed it down to the A/C Amplifier, but would like some input as to where I should go next. So far, this is what I’ve confirmed ok. I’ve grounded the compressor clutch circuit and had relay engage as well as activate the compressor clutch (my compressor is currently shot, so there is a test light in its place for diagnostic purposes). Next, I checked the continuity of the Dual Pressure Switch, which has continuity, and it passes battery voltage to the A/C Amplifier. The ground has 0 volt drop, and the command signal from the Heater Control Assembly is 0v when the switch is engaged, with battery voltage disengaged.

Now the bad, pin 5 of the A/C Amplifier has a constant 0v, which according to the EWD should have battery voltage when the key is on. Second there is no voltage coming out of pin 11, which is a pull up resistor and the ECM grounds to activate the compressor clutch.

When I apply battery voltage to pin 5 the condenser fan and the compressor both operate key on, A/C button engaged or disengaged, and there is still no voltage on pin 11. So, I’m leaning towards needing a new A/C Amplifier, but I’m still unsure.

I believe that’s all of what I’ve done so far, any other suggestions would be greatly appreciated. If you need any other info I’ll be glad to provide it. Thanks in advance!

 

[jetjock]

Pin 5 is the power supply to the amp. You need to find out why it's not getting 12 volts. Since it's powered from the same place as the dual pressure switch, and you claim it's passing power to the amp, the problem should be simple to resolve.

Pin 11 is not the input used to activate the compressor. It's an output to the engine ECU for AC idle up. Pin 2 is the AC enable signal from the heater control panel.

Also check to be sure the water temp switch input on pin 8 isn't low as that'll keep the compressor off. It's all moot until you get power on pin 5 though...

 

[maj75]

My AC was not working, I could tell by looking that the compressor clutch was not engaging. Took it in thinking that is was the clutch or compressor. Shop put in freon and the AC works perfectly. I don't know how the climate control system knows whether there is enough freon, but it does. The shop said that if the freon gets too low, the system will not engage. It worked for me YMMV.

 

[Dirgle]

There is a pressure switch on the passenger side of the engine compartment that can tell if there is enough refrigerant in the system. The OP says this switch is passing continuity which indicates that the system has enough to at least operate.

 

[tye-bo]

I've been trying to track down the circuit to pin 5 (doesn't have power at L1, so I'm thinking it may have a bad splice further up). The thing is that once that circuit behind the HVAC unit, I have no way of tracking the circuit. My next step is going to be pulling the fuse and checking from there, but I have a feeling that it won't be passing voltage. Any ideas on where the splice is?

 

[jetjock]

It's in Relay Block 4. Right kick panel. Same block as the AC fuse which supplies its power.

If you mean the 10 amp AC fuse that can't be the problem...

 

[tye-bo]

I was refering to the CIG fuse in the left relay block. According to the EWD (I'm using the 87), the dual pressure switch and the A/C Amplifier are power off of it. But, I will check the other side, because Toyota has been known to mis-publish info before. I appreciate the help!

 

[jetjock]

Hmmm. I'm looking at an 87 EWD as I write this and the only thing the CIG fuse does is power the coil on the clutch relay. The 10 amp AC fuse powers the amp and feeds the dual pressure switch. Regardless, if the switch is passing voltage to the amp as you claim whatever fuse is involved must be good....

 

[tye-bo]

I stand corrected, it is powered off of the A/C fuse, I apologize for the misunderstanding. That would explain why there was a 12 volt drop b/w the CIG fuse plug, and pin 4 of the A/C amplifier. Never question the JetJock

 

[tye-bo]

Ok, so it is now fixed. After digging around behind Relay block #4, I found that there was continuity between the fuse port and pin 5 of the A/C amplifier. I thought it was quite odd, so I looked at the fuse and it was Blown! I replaced the fuse and everything is working. Now I just need to figure out where and how pin #4 is shorted to power. Thank you for all the help, and lesson learned (again) always check the basics.

 

[jetjock]

Always happy to help someone who appears to know what they're doing even if they do turn out to be a bit sloppy. The clueless, not so much...