Diesel AC Amplifier Red Knob Adjustment?

[doug720]

I am using a 12v diesel AC amplifier from a HJ or BJ60 I sourced in Canada.

Recently, I was having an intermittent AC issue and found the AC amplifier connection was loose...easy fix.

But while I was there I removed the AC amp board and cleaned all the connections. That is when I saw the Red Knob! I remember seeing this when I did my swap, but promptly forgot about it.

What does this knob do? Mine is adjusted about 75-85% towards the clockwise stop.

Any advice? Does it work the same a gas model for compressor clutch engagement rpm adjustment?

Thanks

Doug

 

[Dougal]

AC amplifiers are just thermostat control to stop the AC evaporator icing up. I'm guessing that's a temperature adjustment, it may be fine adjust or it could have a decent range.

I'd stick a thermometer in a vent, run the ac on full noise and see what impact the adjuster has. Mark it's original position with a paint pen first.

 

[doug720]

Dougal, thanks for info on amplifier, I will try those ideas. But. my AC issue is getting more involved.

I thought I had a bad connection at the amplifier, no too easy.

General info:

1) System is a combo - All stock Toyota FJ60, except for:
A - Isuzu 134 compressor
B - Custom hoses
C- Toyota 60 series diesel AC amplifier

2) System was professionally vacuumed and filled with R134
A - Receiver was a year old and had been running 134


Here's the symptoms:

1) When AC is first turned on, all is good. Cold air and no issues.
A - Big pipe at firewall is nice and cold
B - Little pipe at firewall is warm
C - Good flow at receiver glass window

2) After a few minutes, warm air only and no power to compressor clutch.
A - AC dash light is on
B - Big pipe at firewall is warm
C - Little pipe at firewall is warm
D - No change if parked, moving or 65 MPH
E - Clutch will not engage unless engine has been off for a long time
F - I can jump compressor with 12v and it will run and be cold

I have been reading the FSM and see all sorts of possible issues; expansion valve, too much or too little refrigerant, thermistor, pressure switch, etc, etc. But none reference an intermittent clutch engagement?

I'm lost. Any suggestions

Thanks

Doug

 

[davegonz]

Here I though that the AC amplifier increased the RPMs when the AC clutch engages. So you're saying it's only a control board for over pressure and temperature switches?

 

[davegonz]

Here's what the gas version does, but no mention of the red dial.

The chassis manual has a nice section on the AC system, even diagrams the circuit for you. the "magic blue knob" does exactly as mentioned, adjusts when the amp will let the clutch engage in regards to RPMs.
Clockwise=lower RPM
CCW=higher rpm required to run the AC.
The amp gets a signal from the coil, same wire as the tach, that it reads for RPM.
Thermister and pressure switch functions are also controlled in the AMP, it all come down to telling the compressor when to run and when to shut off.
Just remember that to bypass the entire amp just jump the yellow wire to the black with white wire and the clutch will engage when the AC button is pushed, disengage when the button is out.

Can you bypass the amplifier like what Kevin mentions above and see if that keeps your AC on?

 

[Dougal]

Here I though that the AC amplifier increased the RPMs when the AC clutch engages. So you're saying it's only a control board for over pressure and temperature switches?

In most AC systems it's just a thermostat to stop icing up of the evaporator. Not even a pressure switch (that is seperate and usually on the filter/drier tank).

Any idle-up system is usually connected to the compressor control circuit. So it only idles up when the compressor is clutched in. How is the idle increased on the toyota diesels? Is there a vacuum actuator somewhere?

Doug, I would stick your multimeter across the pressure switch (if it has one on the filter/drier tank) and then the amplifier outlets to see how they are behaving. This can at least rule out one of them.

If the worst comes to the worst, simplify the system and bypass the stuff you don't need.
AC on/off button (you've already got), fan interlock, thermostat amp and pressure switch. My Isuzu engine doesn't idle-up with AC and it's never bothered me. I don't think my diesel work car does either (but it's out at the moment).

 

[davegonz]

Good info Dougal. My 4BT set up is the same as your Isuzu. No idle up. I just have the idle adjust a little higher to compensate for the AC being on. In Texas, that's 90% of the time

I seem to remember having to jump my AC amplifier (via the yellow to black/white wire mentioned above) back when I had my green 62 (Princess) with the 4BT. It worked fine.

 

[Dougal]

One of the best parts about my current setup is a dash adjustable thermostat on the evaporator. Slide it along to your comfort level and it holds the outlet temp steady.

I have hacked into the AC system on my work car to give it a four position switch (std, colder, colder still and arctic breeze). The factory AC in that was putting out air at 10C. Which is fine for defogging windows, but isn't enough to cool down a hot car in summer.

 

[doug720]

FIXED MY AC!

I checked things out again today and had the same problem, it worked a few minutes, then the compressor clutch wont engage. While messing around the with the plug to AC amplifier, it made the clutch lock up, but I could not keep it that way.

Well, I decided to go see my AC guy to see what he thought the problem was. We checked all the switches and electrical - all worked right, correct pressures, no bubbles, etc.


Then he started to check the amplifier and the clutch kicked in? Could it be a bad amplifier? Yes bad plug from a corroded used diesel amplifier I bought on mud! It looked kind of corroded when I opened the box, but I was assured it worked...NOT!

Believe it or not, my AC guy had a Toyota AC amplifier board at his shop! It was a little longer than the 60 board and it was from a gas model, but the plug was the same, so we plugged it in...Oh Yes, everything worked perfect, 32 degree air at the vent, compressor cycles as it should, start - stop and it keeps working perfectly!


The amplifier as I said is a gas model from something Toyota with the idle up feature, which is not supposed to work without a coil signal, but it does and I found out why!

I used the stock 2f coil signal wire to connect the hall effect injection pump sensor on the 4BD2 to run my tach with a Dakota Digital signal convertor. This sensor must mimic the coil signal and make the gas amplifier work.

This may be good news for other 4BD2 swappers who choose to the Isuzu IP rpm sensor on their 60's.

Long story, but a cold happy ending for me.
Doug

PS - The new board has the same red knob as the diesel board and has the idle knob on top! Original question...What does the red knob do?

 

[Dougal]

Great news.

I still have the original answer to your original question. Try it and see.

 

[doug720]

I'm afraid to try adjusting it...It's already 32 degrees! It felt like I could store meat inside on the drive home LOL!

I will try moving it this weekend and see what happens.

Thanks to all who gave their time to help on this.

Doug

 

[Adam B]

How is the idle increased on the toyota diesels? Is there a vacuum actuator somewhere?

Yep. When the compressor clutch is engaged a VSV is activated (off the top of my head I think they're actually wired in parallel), vacuum is applied to a diaphragm, a little rod is pulled by the diaphragm, and the rod mechanically moves part of the throttle assembly on the side of the injection pump.

 

[doug720]

As I have to go to Palm Springs tomorrow for work, might as well give the AC system a trial by fire and take the 'Cruiser! It's forecast to be 107f! That will give her a good workout.

Doug

 

[voodoobillyman]

On the 40 series that themostat adjustment is on the left side of the control box, with a hole to adjust. it shows on a sticker to turn it clockwise for cold. At 32 Deg. at the vent you might need to turn it counter clockwise to prevent it freezing up. It controls how long the clutch is engaged on the compressor. That compressor is better than the stock Toyota unit, the adjustment would have to be adjusted all the way clockwise with 60 deg ambient temperature outside for me to get close to that.

 

[doug720]

Well it still works like a champ! Palm Springs was not near as hot as expected...It was only 98f!

The AC worked great, in fact I never ran the fan above the middle position all day. No freeze ups, the compressor cycled like it is supposed to, so I'm leaving well enough alone!

VooDoo, thanks for the info on the red knob, If issues come up I know what to do now. Funny the FSM does not show that knob?

Thanks all.

Doug