Gleaner M2 A/C questions

My dad has a M2 Corn and Soybean Special that we're working on the A/C system.. The previous technician that came by just seemed to add more refrigerant to the system and it worked for about a day or two. I own enough diagnostic tools to figure this out but I need help.

I would say expansion valve is bad. Replace expansion valve and receiver drier, pull a vacuum, and recharge.        MACK

Evidently you have a multitude of issues.  First IF the system had 80 # - you have a bad low pressure or high pressure valve.  The low pressure opens  and breaks the circuit at say 30# ish  and the high side will open at the high 300's depending on valve.  80# is about right equaled on a hot day.  When the clutch engaged you should have seen some difference in pressure even if the valve is stuck open.  Unless the hoses have been replaced with barrier hoses R134 will seep out the hoses and a small recharge will be necessary probably every 30 60 days.  IF the unit has been sitting - the compressor shaft seal will probably be seeping as well.  The other issue is the condenser core - almost all the ones I have ever seen need about an hour of pressure washing - really - they may look clean .. but... If you do not have a strong air flow from the cab blower - it is probably clogged as well.  A dirty  condenser will cause high pressure and a dirty evaporator will freeze over.   As stated , change the drier and expansion valve , pull a vacuum for at least 15 minutes,  let it set for at least 10 minutes to check for a leak - it probably will leak at the fittings from the high side hose fitting crimps - grab them and twist to see if they are loose.  Many times the system will hold a vacuum then leak under pressure at these places.   Charge the system with liquid  until it will hold no more, then turn the can or cans to vapor to finish the charge when the compressor kicks on. Don't listen to anyone about pounds of charge - go by pressures.  The high side on a 80-90 degree   should be 225 PSI -  + or - 10 psi.  The low side must be below 20 psi to be cold.  Do the charge with the fan on high.  Then shut off the recirculation lever to max recirculation and turn the fan on low with door shut - the low pressure should drop to 10 to 12 psi and the thermostat should click the clutch out.   IF you see the clutch clicking on the off - it is overcharged or a bad HP switch.  The fans on the condenser core should be on when the compressor is on.  I have seen a few units where the  thermostat wire is trying to run the compressor and fans - this will not work.  The thermostat wire only triggers and relay that powers both fans and clutch.  Hope this heals and helps.     

The system worked last year and the local Allis technician came by and hooked up his gauges to the system and ended up adding more R134a to it.. According to my father, it wasn't the coldest but it was acceptable.

Low or high pressure valve? You mean "switches" surely.. 

I suppose I could try lowering the system pressure to below 30psi to see if the compressor will kick-on all on it's own, without bypassing the low/high pressure switches, but when I lowered the system pressures last time, both sides dropped equally and stayed equal while it was running.

I have already cleaned the condenser and it's as spotless as it can be. With the switches bypassed to make the compressor and the condenser fans run, it will easily hold a piece of cardboard against the outside of the condenser box mesh screen.. So I'm getting plenty of air flow through the condenser.

I also took apart the panels in the cab and checked everything was clean around the evaporator, and the cabin air filter is pretty new and not dirty.

The heater valve is working nicely and shutting off hot coolant flow as well.

As far as I know, the system could have so much humidity and outside air in it that it can't condense it, and that could be why the gauges don't show different pressures on either side. Non-condesables.. This is the part I'm not sure on and lack the proper knowledge. Why the gauges are reading equal pressures..

I hate to be throwing parts at it until it's fixed. I do know that the receiver-dryer should be replaced if I open the system for other work, so I'm okay with doing that. It's only $25 and the expansion valve seems to cost about the same, but I hate to be spending my fathers money needlessly..

Edited by Bird76Mojo - 08 Sep 2019 at 6:51pm

CHANGE THE EXPANSION VALVE.      MACK

This may be a dumb question but did you open the valves on the compressor when you put your gauges on. If not you may have been seeing the pressure that was still on your hoses depending on what fittings you have.

Well, the system held vacuum overnight perfectly. Zero leakdown. So today I pulled a vacuum again for about 30 minutes and then I hooked up a can of refrigerant. I couldn't get the system to take very much refrigerant at all, so I bypassed the safety switches to make it kick on.

Once I got the compressor running, it was taking in refrigerant easily. After I got it to take 2 cans, we shut everything off and I hooked the safety switches back up to see if the compressor would kick on when we activated the A/C in the cab. We restarted the engine, turned on the A/C, and it kicked on successfully. My fathers friend is a retired A/C mechanic and he recommended to use 4 cans of R134a in the M2, so that's what I put in the system.

After adding 4 full cans, the A/C was colder than either one of my pickup trucks, and they're very good A/C systems that perform flawlessly. Dad and I were both amazed at how cold it is. It will truly freeze you out of the cab in less than a minute. 

We saved ourselves well over $400 compared to buying the A/C hoses from the AGCO dealer and we didn't have to call the service technician back saving dad even more cash..

So, I'm calling this one a WIN for now. Should it need more refrigerant in the future (I'm sure it will at some point even though it leaked zero vacuum) I plan to add one can with the UV dye in it to pinpoint any leaks for repair.


Thanks for all of the advice and assistance y'all. :)