AC issues with a tractor

shelby27604

shelby27604

Well-Known Member
Joined
Jun 6, 2013
Location
Efland NC
Trying to troubleshoot an AC issue on a tractor, Below is a list of what I have done already.
-Confirmed low side pressure is within spec (30-60psi according to the gauge I am using)
-Confirmed power to the pressure sensor
-Confirmed the Compressor clutch works (with remote 12v power source)
-Confirmed continuity at the AC switch / dial in the cab
-Confirmed the pressure sensor closes under pressure (continuity check)

If I bypass the sensor and jump the pigtail, I can turn the compressor clutch on and off from the switch (as expected)
Clutch on, system set to max cold, I get ALMOST zero change

If I plug the pigtail into the sensor, the clutch disconnects, and the compressor does not spin. Voltage at the battery is 12.4v, voltage at the pigtail is 11.4v and voltage at the compressor plug is 11.0v.

So....my thought is PERHAPS the Evap core is clogged AND my switch is bad? I am not sure if this voltage drop is acceptable, these voltage measurements are tractor not running, but key on (if that makes a difference)

Any other suggestions? I hate working on AC systems.
 
Last edited:
this may help you.

Gauge Readout Tool

Using Gauges for Troubleshooting Gauge pressure is the first tool in AC troubleshooting. The table below shows 7 Gauge Readouts that you may encounter. Use...
www.perrinmfg.com www.perrinmfg.com
 
What is your high and low side pressure when you jump the compressor? When you say tractor are you talking Freightliner or talking John Deere? If it's built in the last 15 years there's going to be a computer involved somewhere
 
Also, metering tubes Vs Expansion valve based systems are totally different fill to volume Vs. fill to weight of refrigerant. More details needed.

At work we have Volvo loaders. You have to fill them to weight and in a “reverse pattern” low side non running compared to high side running. Fuggin Swedes…..
 
braxton357 said:
What is your high and low side pressure when you jump the compressor? When you say tractor are you talking Freightliner or talking John Deere? If it's built in the last 15 years there's going to be a computer involved somewhere
Click to expand...
Tractor as in Ag tractor, Unsure of high side pressure, checked low side with one of those hose gauges included with refill cans ~50psi.

I need to go buy some gauges, but without a recovery tank, vac. pump, leak detector, I see this spiraling quickly.
 
Last edited:
you can get gauges and a vacuum pump reasonably from harbor freight. You can pressurize the system with compressed air to find the leak. The link I posted if for an expansion valve type system like we use on the machines at work.
 
Jeff B said:
you can get gauges and a vacuum pump reasonably from harbor freight. You can pressurize the system with compressed air to find the leak. The link I posted if for an expansion valve type system like we use on the machines at work.
Click to expand...
This tractor is getting ready to be sold, and I just need it done....being honest, I was hoping for a short simple solution that didn't involve a learning curve and the purchase of additional tools (hoping, but not really expecting)...I do have to completely replace the AC on my XJ and I will definitely reference the information above, as that project won't be as time sensitive.

skyhighZJ said:
Also, metering tubes Vs Expansion valve based systems are totally different fill to volume Vs. fill to weight of refrigerant. More details needed.

At work we have Volvo loaders. You have to fill them to weight and in a “reverse pattern” low side non running compared to high side running. Fuggin Swedes…..
Click to expand...
This statement and my complete inability to determine the difference was the nail in the coffin for this project, there is a HD diesel shop down the road, he said he could take on the job, and to drive the tractor there was faster than trailering it anywhere....so fingers crossed it is a quick and inexpensive fix (which it won't be)....but I would never buy a cab tractor without AC, so I would never sell one without it either.
 
That link wont be compatible for an XJ A/C system.
 
Shop just called, apparently there was no freon in the system. It sounds like he has it running cold with some o-rings replaced at the compressor and a jumper at the pressure switch (pressure switch is apparently also bad). I am not sure what my gauge was reading on the low side, but I am happy for the help and happy I didn't spend days beating my head against the wall.
 
Well, I went out to start the tractor today and the AC wasn't blowing cold, I popped the hood and found the compressor clutch quickly cycling on and off (rapidly ~3times/second according to the video I took). The tech that recharged the system and put a new pressure sensor in it said "That compressor is bad".

So I am back, looking for some direction from NC4x4. Before I fire-up the parts cannon, is there any tests I can/should run? Will high side and low side gauges point me towards anything in particular? This system has an expansion valve, does that need to be replaced if the compressor goes bad? Or are there other components that should be replaced in the event the compressor goes bad?

I feel like something obvious has been missed, tech replaced some O-rings at the back of the compressor, pulled a vac. (assuming he held it for a while), found the pressure sensor was bad because he had to jump it to make the compressor run. I drove the thing home with the AC blowing cold.....I haven't fired it up since, and now I have this NEW, frequent cycling, no cold condition.
 
skyhighZJ said:
Compressor short cycling is “almost” always a pressure issue (not enough gas)
Click to expand...
Man....fingers crossed! It would make my day if I am just looking at a recharge and a new O-ring. I called the shop and they said I can bring it back on Monday, I would still like to go in knowing more than they do so....

Talk to me like I don't work on AC at all......I got the gauges from Autozone, and the compressor did function normally for a min or two before it started its rapid short cycle. Do I hook up the high side and low side gauges and the readings right off the bat are representative of the system condition, or does it need to cycle for a period of time?

Am I safe to jump the pressure switch to run the compressor for X amount of mins. or is that going start the compressor chewing itself up?
 
Last edited:
shelby27604 said:
@Jeff B When using your guide, do I jump the pressure sensor circuit to keep the compressor clutch engaged?
Click to expand...
The compressor needs to be running to build pressures. Be careful though, I do not know if your system is expansion valve or orifice. This guide is for expansion valve.

Have you confirmed you don't just have a bad switch?
 
Jeff B said:
The compressor needs to be running to build pressures. Be careful though, I do not know if your system is expansion valve or orifice. This guide is for expansion valve.

Have you confirmed you don't just have a bad switch?
Click to expand...
System is Expansion valve.

Switch was just replaced as a part of the service along with O-rings at the back of the compressor. It is 100% possible I have a bad switch, but I did drive the thing about 20 mins. home without an issue (at least I don't think I had an issue, I was driving not looking at the clutch, but the system was cold).

I get that the compressor needs to be running to build pressures, just wondering how long it needs to be running (is it like an oil pump, if you don't see flow in 5 seconds....something is wrong).

If the compressor is toast, what else in the system would need to be replaced to get the system back to 100%? (As I am selling it, I want it right for the new buyer).
 
When you jump it, what happens with the pressures? The system is it's own atmosphere, fluid into the cab, as it exchanges the heat for cold it turns to a gas. Then is sent to the condenser in front of the radiator to change back to a fluid. So for this to cycle it takes a little time.
Do you have any coolant in the system?
 
The plot thickens, I put the gauges on, turned on the AC and it blows cold, low side pressure is steady at 33 and high side is solid at 215 (low side is a little high according to the guide supplied). No clutch chatter, going to do a longer test today and see if I can recreate the issue, feels like I need to be looking for a pinched wire somewhere in the clutch circuit? Unless the AC Gurus see an alternate option.
 
shelby27604 said:
The plot thickens, I put the gauges on, turned on the AC and it blows cold, low side pressure is steady at 33 and high side is solid at 215 (low side is a little high according to the guide supplied). No clutch chatter, going to do a longer test today and see if I can recreate the issue, feels like I need to be looking for a pinched wire somewhere in the clutch circuit? Unless the AC Gurus see an alternate option.
Click to expand...
If it’s a very small system they could have overcharged it and hooking the gauges up took just enough gas out. I see a lot more issues with ac lately being too much oil. I know it’s not your issue but so many people run the Freon that’s full of dye and clogs the system up.
 
Noel said:
If it’s a very small system they could have overcharged it and hooking the gauges up took just enough gas out. I see a lot more issues with ac lately being too much oil. I know it’s not your issue but so many people run the Freon that’s full of dye and clogs the system up.
Click to expand...
I was using the Autozone rental gauges.....the o-rings were a little worse for wear and I did see some dye leak out of the high side fitting (~2 teaspoons worth if I had to guess). The supplied specs for the system in the manual are not super clear, so maybe it was slightly over filled by the shop? I will do a long run test and check for electrical issues, if everything checks out, I guess I will have to assume I was looking at a slight overfill, I really appreciate the additional insight!
 
shelby27604 said:
I was using the Autozone rental gauges.....the o-rings were a little worse for wear and I did see some dye leak out of the high side fitting (~2 teaspoons worth if I had to guess). The supplied specs for the system in the manual are not super clear, so maybe it was slightly over filled by the shop? I will do a long run test and check for electrical issues, if everything checks out, I guess I will have to assume I was looking at a slight overfill, I really appreciate the additional insight!
Click to expand...
Yea people get happy with that dye for some reason. Hopefully you get it straightened out
 
Ran the tractor for 30 mins at various operating RPM with zero issues, compressor clutch stayed on, system was cold, what I found is at idle the clutch will come on and off (not as frequently as before), no gauge info to report during the idle chatter (but I can toss some gauges on tomorrow if there is some value to that information).

The manual recommends turning the tractor off rather than letting it sit at extended idle, (assuming this is emissions related) so I am wondering if this is Normal for the system, or if I still need to work on system freon levels....experts chime in please!
 
Your compressor should cycle. Depends on the size of the system and a bunch of other parameters as to how often it cycles. By no means should it be on/off/on/off type of situation though. Should be on to work, then off to rest. Think of a well pump with a garden hose running. Pump kicks in, fills pressure tank, pump kicks off. Pressure tank bleeds down, pump kicks on to restore static pressure. Sort of apples and oranges but the concept of cycling is the same.
 
I'll bet one og the pins on the pressure switch was not making contact or was pushed in a bit. When you pulled it to jump the compressor on and reinstalled it contact was made. Seen this so many times, especially in CAN systems
 
Well, back to the shop today, AC gauges hooked up, found the high pressure side running above the switches high spec at idle, but pressures were well within spec. at all other RPM's. Tech feels confident we need a new expansion valve. The valve is buried inside the canopy, but it looks like I can take the clam shell off with a couple bolts, and access SHOULD be pretty straight forward.

AC blows cold, defrost worked the whole trip there and back....I think we are on the right track, this is probably nit picking....the odds of prolonged usage at idle is probably zero, but I can't sell something that I advertise as being 100% if it isn't just that. Will post back with results once the new valve gets delivered/installed.
 
New expansion valve is in, and the issue is still present (excessive high pressures causing a short cycle on the clutch). Testing at 82 deg. and multiple temperature settings and fan speeds in cab (same results)

System is cold, but not ICE cold

System capacity is not noted in the manual, tech put 1.25lbs and first, and took it as low as 0.5lbs in the system and the problem still continues, currently the system has 0.8lbs in it.

High side pressure switch is 100% controlling the system now, closed (clutch on) at 30psi, open (clutch off) at 450psi.

I read through the link @Jeff B posted, and I do not see any options that fit exactly, excessive refrigerant seems close, but knowing the system has been as low as 0.5lbs makes me think that is not what we are looking at.

Is this the kind of readings you get with a system with too much UV dye in it? Does a full evac get all that out? At this point, I have paid this tech too much to do too little....but I would also prefer to not rent a trailer to drag the tractor somewhere, maybe a mobile tech can vac and refill? Quickest option that points me toward a solution, I have a good set of gauges now, confident the system holds a vacuum.
 
Last edited:
Back
Top