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986 A/C question


tmarch
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The A/C on my 986 works pretty well for 20-30 minutes and then starts blowing warm air. I havent checked pressures yet. Wondering if low refrigerant would cause this or something else? I blew out both cab filters and it didnt make any difference. Anything else I should check? Thanks.

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Have you shut off the heater valves at the engine. Sometime the shut off in the cab doesn't shut off tight enough to stop hot water from circulating. Also would get gauges on to see what the pressures are.

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8 hours ago, mrfred54 said:

Have you shut off the heater valves at the engine. Sometime the shut off in the cab doesn't shut off tight enough to stop hot water from circulating. Also would get gauges on to see what the pressures are.

I capped off the heater hoses on 3 three tractors found 5 of 6 valves leaking . 

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I would say 3 things.  1) freeze up, but usually airflow will decrease as well 2) something electrical giving up the ghost when it warms up getting current run through it (thermostatic switch , pressure switches or compressor clutch) 3) the system gets saturated with heat from the evaporator and the condenser cant shed it due to dirt and or lack of airflow.  This will show up as really elevated discharge pressure.  

Doubt its a low charge as it shouldn't work very well right off the bat.  

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You need to check out the system with guages. You can leave them on while you run it if you attach them very securely.

When it stops working does the ac light illuminate?

Is the compressor still running?

Thx-Ace 

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I've had freeze up issues before which is why I blew out cab filters. Air flow does not decrease at all. Refrigerent light does not come on, and I'm sure the ac clutch is engaged, but I guess I havent watched it enough to see if its actually cycling. I wouldnt doubt the system could be low a few ounces, but it works right off the bat when you start it. 

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All above suggestions. Also, is the insulation foam on the cab roof cover so you don't get hot air moving across the top of the evapator?

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Easiest thing to check is to look for frost on the suction line at the compressor.

 If you have frost and no cold at the vents, evaporator core is frozen.

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A bit of further explanation;

If the refrigerant in the system gets low, the pressure; and therefore temperature, of the refrigerant will also be lower.

In a correctly operating system, the temperature of the refrigerant as it enters the evaporator will be right around the freezing temperature of water (32°F). As the air moves over the evaporator coils, the moisture in the air will condense on the coils. This condensation will drip off the coils, and go out the drain tubes.

When the refrigerant is low, the temperature of the refrigerant at the beginning of the evaporator coils will be colder than the freezing point of water (less than 32°F). Because the coils are so cold, the condensation that forms on the coils will freeze. Then ice builds up on the coils, it will restrict the air flow through the evaporator. Because of the restriction, the refrigerant can't absorb as much heat from the the indoor air moving over the coils. This causes the refrigerant to boil later in the evaporator, which causes ice to form further along the coils. This situation continues to progress, until the whole evaporator is frozen. When this happens, the refrigerant will start to boil in the suction line. This cause the temperature of the suction line to drop, and just like in the evaporator, cause the condensation to freeze.

Eventually the freezing works its way all the way back to the compressor, which is where the troubles really start. If allowed to operate in this condition for too long, liquid refrigerant can make its way back to the compressor. If this happens, the compressor can be"slugged" This means a 'slug' of liquid enters the compressor, and being a liquid, is incompressible. Damage follows.

 When the refrigerant level drops too low, the system stops working. So this problem will occur in a narrow zone, where the refrigerant is low, but not too low.

 
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9 hours ago, catman13 said:

have you cleaned the condenser on the back of the cab , if it is full of dirt it wont work right and the system will go high head pressure and trip out the compressor

This is a 986, not 966. 

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My guess is your low refrigerant light is burnt out. Test that first. If your sure it is NOT burnt out then I suspect your thermostatic switch is getting weak and cycling your compressor off when it shouldn't. Reason I say that is any other condition would sling the light on. Low or high charge. Freezing up too. All other mentions above should be checked and done before you want to use it in the summer. 

Imo I would start with 2 things.

1.) Check your bulb to be good

2.) Get some gauges on it. A "general" idea on pressures on a hot day should be around 30 low side and under 300 high side if York compressor.  This is a general numbers NOT in stone. 

If you find out bulb was indeed bad, and throw some charge at it, clean all things above as mentioned she will probably work good. 

Just my .02 worth

Oh and remember if your light comes on that means your lockout relay Is energized. The only way to reset lockout relay is to shut off compressor and turn back on. If consition is still present it will go straight back to lockout again 

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as @Missouri Mule said the light bulb is likely burned out, our 5088 light ( same as yours ) will come on hi/low or if there are issues - i ended up having my entire system gone thru last yr. Compressor, evaporator, lines, blah blah blah i think I was in around 2200 bucks 

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2 hours ago, searcyfarms said:

as @Missouri Mule said the light bulb is likely burned out, our 5088 light ( same as yours ) will come on hi/low or if there are issues - i ended up having my entire system gone thru last yr. Compressor, evaporator, lines, blah blah blah i think I was in around 2200 bucks 

The next time I have a compressor fail I'm just buying the whole entire sanden conversion. New everything. Done....  

Not trying to get into a debate about sanden vs York,  however the new kits are much better hoses made for 134a unline earlier 86 series. My tri stripe has newer hoses. Not sure if ih changed them or if they had been changed out along its life. I do have 1 with the conversion already and its hands down colder than my others. Everything is cleaned and kept up to as good of shape as possible. I'm not an AC guy but if we could still use R12 I think we would have alot less trouble. 

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I checked the bulb and it does not appear to be burned out. 

Put gauges on and it appears the low side is at 25 and high side is 150? Am i reading them right? Im thinking its just low on refrigerant. Clutch is running constantly.

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New gauge set and it took a some tweaking on valves but finally got it to pull in some refrigerant. Will mess with itfor a while and let you know.

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Pulled in a whole can of refrigerant. High pressure side is just a hair over 200. Low pressure side seems to hang low, around 10 or so. Compressor clutch isnt cycling yet, just stays engaged. Had it run for a while, air does seem a little cooler, never quit making cold air but it may have to run for a little while longer. Thinking I need to get another can and add a few ounces.

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Yes needs some more,  This is R134A right?  I would like to see about 250-275 on high side and 35 or 45 on low side.  A trick that helps get it into the system is to have a bucket of warm water handy and you can dip the can into the water which raises the pressure in the can and forces it into the system. You can use the gauge low side knob to meter in a little at a time and wait and see how the pressures stabilize after a couple minutes. 

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^^ exactly what he said. I'll push mine to 300 on a smoking hot day out in the sun. You can't do this on a cooler day or you'll overcharge it. Just did that on my 1086. It was 90 out and I ran it to 300. It was cold as all get out but I finally kicked the high pressure cutout after a couple hours in the hay field. I had to back it off a fuzz. My low side never gets much over 35 on any of my 3. Remember these hold a fair amount of freon so 1 can isn't much. Thinking 5 lbs but that may be r12 equivalent.  I always figure on about 3 cans every spring. Every single one of my york compressors leak around the shaft some over the winter. I try to cycle them some to alleviate this but its inevitable. 

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Are you saying your clutch is staying engaged even when your high side goes to 0? If it's as low as you showed in the picture it should be cycling some. I wonder if you need to pull the roof lid and make sure someone doesn't have your pressure switches jumped out. 

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