A/C not engaging

Orchardman · Jul 9, 2013

Hi there

my apologies if this has been covered in previous threads but im in a bit of a pickle. I have a Landini Rex 100 GT and have been experiencing A/C issues.

When I bought the tractor, I was under the impression that the A/C worked but the compressor wouldn't hold a vacuum. When I pulled a vacuum and put some R-134a in it, everything ran smoothly and I got cold air but of course all the coolant leaked out (You could see bubbles on the compressor itself). I argued with the company that sold it to me and they agreed to send me a replacement compressor. I also went ahead and ordered a new receiver/drier complete with a pressure switch. Before I installed the compressor, I cleaned the system thoroughly as I could, re-installed the new drier, switch, and compressor and pulled a nice long vacuum to rid the system of any moisture.

When I put R-134a into the system, the clutch doesn't engage, even though the filler gauge lists the system as being fully charged and I see movement in the sight glass. I didn't put too much refrigerant in im sure of that.

I can jump the compressor and when I do, the pressure on the low side drops from the upper 30s to close to 10 or less, even close to zero.

Does anybody have a general method of ruling out possible failing points on A/C systems that they could lend to me? This tractor seems to have multiple electrical issues with it so I can't really rule anything out.

Kind Regards

Mike

Zebrafive · Jul 10, 2013

Try jumpering the pressure switch and see if the compressor will engage. Sounds like you do not have enough Freon in the system.
Low pressure is related to ambient temperature the system is running at. For 90 degrees the low side should be 45 - 50 psi and the high side 250 -270 psi

ASTROENG2011 · Jul 11, 2013

While not completely familiar with the Landini tractor, I am familiar with AC systems. You said that you installed a new drier with a pressure switch. I do know that there are different pressure switches for different operations. Sometimes the pressure switch is placed on the high side of the system and will prevent current to clutch unless a specific pressure is in the system-- prevents system from operation in case of a lost or low charge ( low pressure cut out). Sometimes the pressure switch is installed to prevent compressor operation in case of excess high pressure ( high pressure cut out). Sometimes the switch can perform both functions ( HPCO and LPCO-- called a binary switch). There is even a trinary switch that combines a binary operation for system protection and an auxiliary actuation circuit for an additional/accessory fan on the condenser. If you can locate a leak finder (Yokagawa, TIF or similar for R-134A) use it to look for leaks. Since you said the compressor had bubbles coming out of it, I am assuming you meant around the shell seams. That would indicate possible over pressure during operation -- possible causes being a clogged or restricted condenser, loose drive belt for fan, bent fan, loss of insulation/seals around the condenser radiator area, etc. You may want to try jumping the switch and checking the charge level in the system with the tractor running on high blower at idle. The pressures listed by Zebrafive above look about right. Total charge for the system should be about 32 oz max. Good rule of thumb is that the temperature drop across the evaporator should be 20-30 deg. Anything greater, is great. Anything less could mean a leaking heat shut off valve or bypass air of a blend door. I am not sure that your unit has a blend door- most automotive systems do. Equipment systems usually use a water control valve to shut off the heater coolant when operating in AC mode. Again, I am not completely familiar with your system but have had my fair share of AC system experiences.

Orchardman · Jul 11, 2013

ASTROENG2011 said:
Since you said the compressor had bubbles coming out of it, I am assuming you meant around the shell seams. That would indicate possible over pressure during operation -- possible causes being a clogged or restricted condenser, loose drive belt for fan, bent fan, loss of insulation/seals around the condenser radiator area, etc. You may want to try jumping the switch and checking the charge level in the system with the tractor running on high blower at idle.

Thanks for all the responses. I have the gauges and I will look at the PSI on the low and high sides like mentioned above. I forgot to mention that the compressor is brand new as is the receiver drier. That was when I played squeaky wheel with the company that sold me the tractor. The pressure switch is on the drier unit and is has a low and high cutout.

With the suggestion to jump the pressure switch and measure pressure, this is a dumb question but just jumping the compressor will accomplish the same thing right? just don't want to be wrong with that. Are the pressures listed above for when the compressor is engaged or idle? I imagine engaged b/c the highside probably won't read if its not compressing but just letting my green show. Thanks again for all the help.

Tx Jim · Jul 12, 2013

I agree with Z5 that more freon is required. Jumpering across at the pressure switches or compressor accomplishes the same thing to check freon charge. The pressure's that Z5 gave are with compressor engaged. With compressor at idle the gauges will equalize at about 150 psi each.

murphy1244 · Jul 12, 2013

Did you weigh in your charge?

Zebrafive · Jul 12, 2013

Orchardman said:
Thanks for all the responses. I have the gauges and I will look at the PSI on the low and high sides like mentioned above. I forgot to mention that the compressor is brand new as is the receiver drier. That was when I played squeaky wheel with the company that sold me the tractor. The pressure switch is on the drier unit and is has a low and high cutout.

With the suggestion to jump the pressure switch and measure pressure, this is a dumb question but just jumping the compressor will accomplish the same thing right? just don't want to be wrong with that. Are the pressures listed above for when the compressor is engaged or idle? I imagine engaged b/c the highside probably won't read if its not compressing but just letting my green show. Thanks again for all the help.

Pressures are with compressor running. Only reason I suggested jumpering the pressure switch was you said in your original post that you were not sure if other electrical issues were the cause of the compressor not engaging. If jumpering the pressure switch lets the compressor engage it would rule out other electrical problems. So yes, just jumpering the compressor will get it running to check pressures/add Freon.

Zebrafive · Jul 12, 2013

One other thing; did your new compressor come with oil preinstalled? Did they tell you how much oil the system should have?

Orchardman · Jul 15, 2013

Sorry I got off track there. Okay, to answer some questions. I haven't weighed my charge, I have been using 12 oz cans from the auto store. It did come pre-oiled and I turned the compressor a few times before I engaged it so it wouldn't lock up on me.

I took my pressures this time while I tripped the compressor and this is what happened. At rest, the low side is sitting around 59-60 and the high side sits to about 100. When I engage the compressor, the low side goes down to nothing and the high side goes up to about 150. I don't even get a moderate amount of cooling going on.

It sounds like I still have a low system charge overall. so I should add more R-134a until both sides equal out at about 150 psi at rest? I just don't want to add too much and blow something up.

banjodunn · Jul 15, 2013

G'day add some more charge with the comp running until you see 2-220 on the high side and see what happens you may have a blocked TX valve though

Oh and jumping the pressure switch will tell you if the rest of the elecs including the thermostat is working correctly as the comp should cycle on and off as it gets to temp

Jon