Two Basic AC Questions

[dunnyboy]

I am going through the troubleshooting process on my AC and have been gleaning info from previous threads. Two basic questions:

1. Where is the low pressure switch / sensor located? and can it be bypassed safely if I know I have a good charge in thge system. I'd like to be able to determine if it is operating properly.

2. Now that I have the AC amplifier located, how is it correctly removed / replaced with a spare I have now located?

 

[1972FJ55]

I am going through the troubleshooting process on my AC and have been gleaning info from previous threads. Two basic questions:

1. Where is the low pressure switch / sensor located? and can it be bypassed safely if I know I have a good charge in thge system. I'd like to be able to determine if it is operating properly.

2. Now that I have the AC amplifier located, how is it correctly removed / replaced with a spare I have now located?

I can answer #1, the switch is inside the evaporator case. You can bypass it to test the system, but I wouldn't leave it bypassed long term. Sorry but I'm no help on the amp.

 

[dunnyboy]

Thanks for the info. No, I do not planto bypass it long term, I may need to bypass to test it. Thanks again.

 

[doug720]

On the amp, it's located below the glove box in a pocket molded into the evaporator case. To remove it, there is an external clip you release and push the amp up and out. You also unplug the wires from the amp with a clip on the top of the amp.

Do not turn the knob on top of the amp, as this is adjusts the idle up speed. There is also another lower adjustment to

If you follow my swap link below and check page 10-12, you will find a ton of AC related info.

Hope this helps

Doug

 

[FJ40Jim]

To be clear, the blue knob adjusts the minimum idle speed that will allow AC cut-in. If the engine is idling at 600RPM and the cut-in speed is adjusted to 625, then the AC will not engage at idle, but will kick on as soon as the vehicle starts to drive away from a stop, very annoying.

The actual idle-up RPM is adjusted by the linkage screw on the front of the carb.

 

[Jlosquared]

Why is it recommended I don't mess with the knob up top (I figure this is the blue knob)?

May be too late as I messed with it today; really hot day in SoCal and the A/C normally wouldn't engage when idling so, I turned the knob until it did. Now if the AC is on an I'm idling it actually blows cold air, as opposed to having to be moving to get cold air...

Other that possibly overheating, what are the repercussions?

 

[Elbert]

none that I know of...I think the warning had to do with getting the amp out whack in regard to idle rpm.
Truck should not overheat simply due to A/C operation.

 

[FJ40Jim]

The point of the blue knob is to inhibit AC engagement at low RPM, to avoid stalling the engine if it is idling too low.

The blue knob should be set to give a minumum engagement RPM of 625, then adjust carb idle RPM to the sticker setting of 650.

 

[Jlosquared]

Thank you, that's a relief.

The truck seems to drop about 50 rpm (to about 650) from its idle (looks like around 700 from eyeing the gauge) when engaging the A/C..doesn't feel like it'll stall but if it does...ill know now where to look.

 

[camnowell]

sweet glorious day

To be clear, the blue knob adjusts the minimum idle speed that will allow AC cut-in. If the engine is idling at 600RPM and the cut-in speed is adjusted to 625, then the AC will not engage at idle, but will kick on as soon as the vehicle starts to drive away from a stop, very annoying.

The actual idle-up RPM is adjusted by the linkage screw on the front of the carb.

Jim, you just saved me a trip to the shop to service my AC thanks to that little tidbit of information. Knew about the knob, but didn't know its function. 30 seconds later and now my AC blows ice cold at idle. Thanks!

 

[FJ40Jim]

Thank you, that's a relief.

The truck seems to drop about 50 rpm (to about 650) from its idle (looks like around 700 from eyeing the gauge) when engaging the A/C..doesn't feel like it'll stall but if it does...ill know now where to look.

Cruisers with Nippondenso AC system have a vac operated AC idle up linkage on an Aisan carb. It will raise the idle speed when the AC compressor kicks in.
Post a pic of the carb and the driver side inner fenderwell and somebody can point out where the vacuum pot & VSV should be located.