Another AC question

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

Loober

Loober

10 Year
Joined
Jul 5, 2013
Threads
114
Messages
957
Location
San Diego
Can someone chime in on the ins/outs of the 90s era 70 series AC controls. Upon purchasing my 77 it never had functioning AC, turn the switch, air would blow but never got cold, didn't bother looking into it much more then that.

Since swapping in the FT motor I've been determined to get the AC working, replaced condenser, drier, got everything button up, vacuum tested, and began charging system, at that time noticed the AC clutch was not engaging. Checked power at the wire to the compressor and nothing. Pulled the dash apart all the wires seemed to be there and connected nothing was visibly wrong.

Decided just to wire a separate switch to activate the compressor, clutch turned on, charged the system, AC got cool but never cold.

Couple questions:
- The constant switch to the compressor cause it to always be engaged and not cycle, any drawbacks to that.

-Noticed the cruiser has an AC module, does that control something else, like a thermal valve of sorts at the evaporator? Thinking the reason the stock AC switch isn't working has something to do with that not working also?

Compressor seems to be working, reading low and high pressures based on what it should be for a 134a system.

BTW does anyone have specs on exactly how much refrigerant a 77 system takes, I could not find anything, kind of guessing based on low/high pressures. The system was originally R12, converted to R134a since the FT came with a 134a compressor, not sure if weights are the same for R12 and R134a.

Thanks
 
The weighed in charge for vehicles changed over from R12 to R134a aren't the same.
Depending upon outside air temperature; the suction pressure should be approximately 35psi and the discharge air temperature would be 40 to 50 also depending upon outside air temperature.
After the A/C operating for a while you would expect to see the suction line coming thru the firewall to shows signs of frosting.
The 1993 PZJ75 that I have in the PI has R134a, but there is no tag listing the charge or oil quantity like the vehicles in the US.
 
Loober said:
Couple questions:
- The constant switch to the compressor cause it to always be engaged and not cycle, any drawbacks to that.

-Noticed the cruiser has an AC module, does that control something else, like a thermal valve of sorts at the evaporator? Thinking the reason the stock AC switch isn't working has something to do with that not working also?

Compressor seems to be working, reading low and high pressures based on what it should be for a 134a system.

BTW does anyone have specs on exactly how much refrigerant a 77 system takes, I could not find anything, kind of guessing based on low/high pressures. The system was originally R12, converted to R134a since the FT came with a 134a compressor, not sure if weights are the same for R12 and R134a.

Thanks
Click to expand...

You don't want the compressor running full time. The part on the evaporator is a thermistor. There's also a pressure switch on the evaporator. You want both of those working, luckily 60 series parts of the same year are the same. Expansion valve is in there too, I haven't changed mine but I'd imagine 60 series stuff works. On my HJ75 I just added freon until my gauges read proper pressures for my temperature rather than measure weight. This is a nice R134A chart to have.

Temp-pressure-chart-33776F1.jpg


Another thing to check is there is a VSV that has to be wired up properly to allow the compressor to work right. Mine was missing the VSV when it arrived from Australia, but any 80's Toyota VSV is about the same. The wiring diagrams are available online, or if you can't find it I will try and take a pic of my service manual later today. Mine freezes me out on a 90 degree Florida day :) So when the system is working, it works GREAT.
 
@ca18sean Hmm thanks for the info, confirms my fears that there are other electrical parts that may be the culprit. I have the wiring diagram and seen the bits you are referencing, there is a part called the AC amplifier, what does that do? What exactly does the thermistor do. Not sure where to start with the troubleshooting besides just replacing all of them. The other caveat is the truck is 24v, so not sure how easy I can get those replacement parts in 24v.

The VSV valve you mention, that must pertain to the throttle up function correct?
 
Loober said:
@ca18sean Hmm thanks for the info, confirms my fears that there are other electrical parts that may be the culprit. I have the wiring diagram and seen the bits you are referencing, there is a part called the AC amplifier, what does that do? What exactly does the thermistor do. Not sure where to start with the troubleshooting besides just replacing all of them. The other caveat is the truck is 24v, so not sure how easy I can get those replacement parts in 24v.

The VSV valve you mention, that must pertain to the throttle up function correct?
Click to expand...

I would recommend not just throwing parts at it and hoping the system works. I would test the components one by one.
 
Found some helpful info here that I think is close to the same for the 70 series A/C Amplifier wiring

Here goes another frustrating round of find that gremlin.
 
Loober said:
@ca18sean Hmm thanks for the info, confirms my fears that there are other electrical parts that may be the culprit. I have the wiring diagram and seen the bits you are referencing, there is a part called the AC amplifier, what does that do? What exactly does the thermistor do. Not sure where to start with the troubleshooting besides just replacing all of them. The other caveat is the truck is 24v, so not sure how easy I can get those replacement parts in 24v.

The VSV valve you mention, that must pertain to the throttle up function correct?
Click to expand...

24V definitely makes it harder to find parts. I agree with beno, the FSM walks you through testing each electrical component. And yes, that VSV is the idle up for when the AC compressor is on, but I believe any 24V VSV will interchange.

Explain what the AC Amplifier does ?
 
The ac on my BJ74 quit on me last year on my trip West. I knew it was charged witth R12 and could see the clutch working when I hot wired it. I too put a clutch switch in and forced it to come on. I run it for a while, then shut it off for a while cycling by hand. Not ideal.
I am pretty sure the fault is my ac amplifier. I checked all the components a la FSM and they check out but it still doesn't work.
Thermistor senses warm temp. Pressure sensor feels good pressure. AC switch works. But ac won't come on.
I'm gonna keep switching it on/off by hand for the rest of the summer.
 
I was pretty much doing the same thing, but it still didnt cool all that well and lately, its been getting worse, not sure if something else got damaged as a result. It's been really hot lately, and I am not all that motivated to sweat my ass off chasing a gremlin, looks like that will be a project for the fall.
 
I stumbled onto an ac shop that installed new o rings then filled the system with real R12.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom