AC clutch issue

[T4Rscott]

I have a 99 with almost 220k. The manual AC system is acting up. The clutch only engages when the throttle is depressed. It no longer kicks in on its own. I can hear a relay clicking in the passenger side area.

Can anyone shed some light as to what I should look at?

Thanks,
Scott

 

[thegipper]

I would take it to an shop with an AC machine to have it checked. If I had to guess, you probably have a small leak somewhere and you've lost refrigerant. The compressor will not engage if the refrigerant level becomes too low and you're probably right at that threshold.

 

[azrex]

You might try swapping the A/C relay (I think the FI relay is the same) just to confirm the relay is ok.

 

[T4Rscott]

I would take it to an shop with an AC machine to have it checked. If I had to guess, you probably have a small leak somewhere and you've lost refrigerant. The compressor will not engage if the refrigerant level becomes too low and you're probably right at that threshold.

The refrigerant is full and blows cold.

 

[T4Rscott]

You might try swapping the A/C relay (I think the FI relay is the same) just to confirm the relay is ok.

The relays aren’t the same. The clutch relay looks like a small computer board that lives in front of the blower.

 

[LittleCaesar]

Do you have a 12v signal to the compressor when the system is turned on?

 

[Skulking]

I don't have the wiring manual for a 1999, but for a 2000 with manual AC, the wiring manual states the following:

"When the blower SW is set to on, current from the HEATER fuse flows through the A.C fuse to TERMINAL 1 of the A/C dual pressure SW to TERMINAL 2 to TERMINAL 1 of the A/C amplifier. The engine speed signal from engine control Module and the evaporator temp. signal from the A/C thermistor are all supplied to the A/C amplifier. When the A/C SW is turned on, the A/C SW on signal is sent to activate the A/C amplifier. Current flows from the A/C amplifier to the magnetic clutch, turning the compressor on. The A/C operation is shut off when a signal indicating low evaporator temp., or abnormally high or low refrigerant pressure, is supplied while the engine high speed signal exists. When one of these signals is received, the amplifier shuts off the A/C operation"

That would suggest that the A/C amplifier will shut off the AC clutch if engine RPM is too low. Since reving the engine makes the clutch engage I would start by looking at this area. How high do you need to get the RPM's before the clutch engages? It seems like either the A/C amplifier is getting a bad signal, or the A/C amplifier itself is going bad.

 

[T4Rscott]

I don't have the wiring manual for a 1999, but for a 2000 with manual AC, the wiring manual states the following:

"When the blower SW is set to on, current from the HEATER fuse flows through the A.C fuse to TERMINAL 1 of the A/C dual pressure SW to TERMINAL 2 to TERMINAL 1 of the A/C amplifier. The engine speed signal from engine control Module and the evaporator temp. signal from the A/C thermistor are all supplied to the A/C amplifier. When the A/C SW is turned on, the A/C SW on signal is sent to activate the A/C amplifier. Current flows from the A/C amplifier to the magnetic clutch, turning the compressor on. The A/C operation is shut off when a signal indicating low evaporator temp., or abnormally high or low refrigerant pressure, is supplied while the engine high speed signal exists. When one of these signals is received, the amplifier shuts off the A/C operation"

That would suggest that the A/C amplifier will shut off the AC clutch if engine RPM is too low. Since reving the engine makes the clutch engage I would start by looking at this area. How high do you need to get the RPM's before the clutch engages? It seems like either the A/C amplifier is getting a bad signal, or the A/C amplifier itself is going bad.

I have to just barely touch the throttle pedal to get the relay to engage.

 

[Skulking]

I have to just barely touch the throttle pedal to get the relay to engage.

What is your idle rpm in both neutral and in drive once the engine is warm? Is there a consistent RPM threshold where the AC will engage and if so what is it?

 

[19963.4lsr5]

It’s interesting Toyota uses a control module with engine rpm to operate the AC.

 

[T4Rscott]

Do you have a 12v signal to the compressor when the system is turned on?

Not sure. I tried going from the battery to the connector using a lighted tester. The tester lit up, but did not activate the clutch.

 

[T4Rscott]

What is your idle rpm in both neutral and in drive once the engine is warm? Is there a consistent RPM threshold where the AC will engage and if so what is it?

I only need to move the pedal about a half an inch. The idle is normal both in warm up and at normal temperature

 

[brillo_76]

The 1999 Manual AC EWD in a PDF

 

[alumarine]

Have you checked your alternator output at idle?

 

[LittleCaesar]

Not sure. I tried going from the battery to the connector using a lighted tester. The tester lit up, but did not activate the clutch.

Then usually, but not always, it is safe to ASSUME that everything else is working and that the problem lies at the compressor. You can always take a DVM and see what values you get. Only once can I think of where I saw 12v at the connector for the compressor with the system engaged and the compressor wasn’t the problem.

I would then turn the system back on and if the compressor isn’t spinning, CAREFULLY lightly tap the face of the pulley to get it to try and activate. If it does start spinning, then look to replace the compressor.

Also, when increasing the RPMs, does the 4Runner have to be in drive or can it be in park?opcorn:

 

[nissanh]

The clutch disengages when the RPM is below its idle, I saw it in my 92 corolla. I could not find any issues, and at one point I turned the steering and it increased the RPM, and very next second I heard AC compressor kicking in! Then saw AC comes on with higher RPM. Replaced the VSV valve (idle-up control valve) and all good.

Check your IAC valve. That is what controls your idle-up in the 5vzfe.

On a side note, 2UZFE (landcruiser) has a rpm sensor in the compressor! It checks the compressor RPM with engine rpm. If those are not related, ECU disengages the compressor!