AC help desperately needed (2 Viewers)

[SUMMIT CRUISERS]

Of course it's hot here, (triple digits). Vehicle 92 FJ80 Getting ready for a long trip and need AC desperately. Any help or ideas would be greatly appreciated.

Started this thread a few days ago https://forum.ih8mud.com/80-series-tech/497996-ac-fuse-power-source.html. Still no worky.

Symptoms and overview:
No power to AC Compressor clutch.
Compressor functions fine if 12v is applied from battery (blows cold).
Had no power to AC fuse and placed a jumper across the sensor harness that goes to the evaporator. Now I have AC fuse power.
Removed and inspected AC amplifier board. Looks fine with no burnt spots.
Checked AC switch operation. Relay on amplifier board clicks in and transfers power from yellow wire with red stripe to yellow wire with red dashes.
Low pressure switch has been previously bypassed.
Vehicle now has no idle up when AC button is depressed. Vehicle takes longer to start now since this happened.

2 other sensors that I've read about may be to blame. I think one is an engine temperature sensor and another is a neutrual safety switch or starter cut off switch. Not sure where these are at and if they could cause the problem I'm having.

Thanks,

Steve

 

[Dave 2000]

temp sender is possible but not the neutral safety switch AFAIK, the PCB does not always show faults by burning ect, it could be a transistor or cap ect, is it possible to borrow the ecu from a friend or fellow mudder so you could discount that as the culprit?

regards

Dave

 

[CJF]

By "no power to compressor" I assume you mean no power to the magnetic clutch? The clutch itself has a simple ohmmeter test if that's helpful.

 

[SUMMIT CRUISERS]

Dave,

Where is the temperature sensor located? I do not have an extra ECU available to swap out.

Thanks

 

[SUMMIT CRUISERS]

By "no power to compressor" I assume you mean no power to the magnetic clutch? The clutch itself has a simple ohmmeter test if that's helpful.

You're correct. No power to AC clutch. However; the clutch will engage and the compressor will work if I apply 12 volts from battery. AC blows cold then.

I just don't know what is stopping the 12 volts that is coming from the AC amplifier to get to the clutch.

 

[1972FJ55]

We've seen the amplifiers fail. Not common, but not unheard of. Anybody local you could swap with?

 

[SUMMIT CRUISERS]

No, I do not have one. Does anyone have voltage readings for the pins?

We've seen the amplifiers fail. Not common, but not unheard of. Anybody local you could swap with?

 

[Dave 2000]

I assume your A/C guys has double checked the high and low pressure settings? The compressor will not engage unless the pressures are correct, blowing cold air indicates there is some gas but does not confirm that the pre required pressure is at the sensor to allow the ECU to let the compressor engage.

regards

Dave

 

[Dave 2000]

Dave,

Where is the temperature sensor located? I do not have an extra ECU available to swap out.

Thanks

Sorry cannot help you with the where as your car is petrol right? My experience is more with the european diesels where it is just under the inlet manifold. If your is petrol the it may take it's reading from the same sensor that controls your fule injection duration ect to the engine ECU.

regards

Dave

 

[SUMMIT CRUISERS]

I assume your A/C guys has double checked the high and low pressure settings? The compressor will not engage unless the pressures are correct, blowing cold air indicates there is some gas but does not confirm that the pre required pressure is at the sensor to allow the ECU to let the compressor engage.

regards

Dave

It's my understanding that by bypassing the low pressure switch the compressor will continue to operate at whatever freon level/pressures are there. If too low, the compressor just locks up. Mine has been bypassed for about 5 years. Is there another sensor that detects pressures other that the low pressure switch located behind the left side head light next to the dryer?

 

[1972FJ55]

The switch located by the drier is a trinary switch, so it senses both high and low pressure, and will shut the compressor off if the pressure is out of spec in either direction. Have you checked for power at the switch?

As for testing the amplifier:

Terminal Specification
6 & ground------------------continuity
8 & 9-----------------------continuity
2 & 6 A/C switch "ON"-------battery voltage
2 & 6 A/C switch "OFF"------no voltage
3 & 6 A/C switch "ON"-------battery voltage
3 & 6 A/C switch "OFF"------no voltage
5 & 6 start engine-----------10-14 volts
5 & 6 stop engine------------no voltage
9 & 6-----------------------1500 Ohms (@25 degrees C)

Another possibility, you may have already checked, is the clutch relay.

 

[SUMMIT CRUISERS]

Ac working now!

Wow,

Just found the problem. The bypassed low pressure switch was not making good contact. I installed a different jumper wire and "wallah" I got 14 volts to the compressor clutch wire and the idle circuit is now working. I have now cut back the wires down from the connector and soldered them together (temporarily).

In conclusion, I had no power at the AC fuse. I bypassed the wiring harness going to the evaporator, got power to AC fuse. Soldered the two wires on the pressure switch together, got my 14 volts to compressor clutch.

I can (hopefully) now enjoy my trip and when I return I will be ordering both bypassed sensors. Thanks so much for all your help. Now it's time to put back the dash, glove box, grill and drivers side headlight assembly.

Anyone know of any concerns about bypassing the "Evaporator" sensor? I know what will happen if the freon gets low with the pressure switch bypassed, just not sure about the other.

Thanks again so much for everyone's help and ideas

 

[1972FJ55]

Bypassing the thermistor that's in the evap box, means the compressor won't cycle off in the event the evaporator freezes up. The results are not good, no flow of refrigerant= no oil to the compressor= short compressor life expectancy.

 

[SUMMIT CRUISERS]

Bypassing the thermistor that's in the evap box, means the compressor won't cycle off in the event the evaporator freezes up. The results are not good, no flow of refrigerant= no oil to the compressor= short compressor life expectancy.

Thanks for the heads up. I'll definitely use the AC sparingly until I get a new thermistor.

 

[Dave 2000]

Glad you got it sorted,


regards

Dave

 

[Rookie44]

Ac working now!

Wow,

Just found the problem. The bypassed low pressure switch was not making good contact. I installed a different jumper wire and "wallah" I got 14 volts to the compressor clutch wire and the idle circuit is now working. I have now cut back the wires down from the connector and soldered them together (temporarily).

In conclusion, I had no power at the AC fuse. I bypassed the wiring harness going to the evaporator, got power to AC fuse. Soldered the two wires on the pressure switch together, got my 14 volts to compressor clutch.

I can (hopefully) now enjoy my trip and when I return I will be ordering both bypassed sensors. Thanks so much for all your help. Now it's time to put back the dash, glove box, grill and drivers side headlight assembly.

Anyone know of any concerns about bypassing the "Evaporator" sensor? I know what will happen if the freon gets low with the pressure switch bypassed, just not sure about the other.

Thanks again so much for everyone's help and ideas

Hey Summit,

*Edited* I have a similar problem and I hoping its identical. Is this low pressure switch, you mentioned, located up in front of the battery tray in the liquid line piping? Did you jump the wires going to this sensor? Or is this somewhere else? You mentioned two sensors/switches that you bypassed. Where is the other one? Did it turn out that both sensors are bad? How can I test these sensors? By bypassing them?

 

[SUMMIT CRUISERS]

Hey Summit,

*Edited* I have a similar problem and I hoping its identical. Is this low pressure switch, you mentioned, located up in front of the battery tray in the liquid line piping? Did you jump the wires going to this sensor? Or is this somewhere else? You mentioned two sensors/switches that you bypassed. Where is the other one? Did it turn out that both sensors are bad? How can I test these sensors? By bypassing them?

The high/low pressure switch on a 3FE is located on the driver's side up stream of the drier. There are two wires that go to the sensor. I bypassed this previously by installing a paperclip into the two wire harness that plugs into the sensor. If you read through the thread I had no power to the AC fuse, no cold air but did have cold air if I applied 12v to the compressor. The problem in this thread was a previously installed bad jumper in the the high low switch and the thermistor located under the glove box to the left went bad not allowing 12v to go to the fuse. I tied the two thermistor wires together and got power to the AC fuse. The only issue was it would get down to at least 30 degrees F through the vents then I had to remember to manually hit the AC button to turn off the compressor in worries of freezing up the compressor. The thermistor regulates the temp that the compressor shuts off. Since then, I have replaced the thermistor and the High/low pressure switch so all is working properly except the compressor finally locked up a few weekends ago after I did the R134 switch in the middle of Wyoming last year summer. New flush, new drier and new compressor are in the works.

 

[Rookie44]

Thanks for the reply! I haven't tore anything apart yet, just been reading and researching. What I know, is that the AC shop charged the system and tested the Compressor. I verified the Compressor runs and the clutch engages when jumped with 12v from the battery and it blows ice. Fan works, system gives a call for cooling...... no voltage to the compressor. I'll try and jump the LPS first. Is there a way to test this sensor without jumping it?

If that doesn't work I guess I'm going to tear into the dash. Before I do that I'll test the fuse. I should have voltage at the fuse upon a call for cool. Right?

 

[SUMMIT CRUISERS]

Thanks for the reply! I haven't tore anything apart yet, just been reading and researching. What I know, is that the AC shop charged the system and tested the Compressor. I verified the Compressor runs and the clutch engages when jumped with 12v from the battery and it blows ice. Fan works, system gives a call for cooling...... no voltage to the compressor. I'll try and jump the LPS first. Is there a way to test this sensor without jumping it?

If that doesn't work I guess I'm going to tear into the dash. Before I do that I'll test the fuse. I should have voltage at the fuse upon a call for cool. Right?

There is no way that I am aware of to test the High/low pressure switch except to just bypass it. The thermistor is accessed under the glove box and up to the left. It contains two grey wires as I recall that are in a black sheathing. No need to tear into the dash unless your AC switch is not activating. The AC fuse will have 12V all the time unless either the pressure switch or the thermistor is bad. Can't remember exactly if its both or one or the other that is responsible for the 12v to the fuse. Just bypass the High/low switch first, check operation and if that doesn't work then bypass the thermistor.

 

[Rookie44]

Will do. Thanks! I read another AC thread last night that told me the AC system is completely different on a 40th. He compared it to a LX450. More fuses to check, things are in different places. You know anything about that? It was late and I'm going to reread it sometime today. I'll let you know about the bypass. I should have some time to look at it this afternoon.

Correction: My 80 is a limited, not a 40th. AC controls are the same as my 93. So it should have all the same AC as the rest of the 80's out there.