air conditioning gets warm

I have a 4 year old Massey 5455 with factory installed air conditioning. When the tractor first starts in the morning the air is just as cold as in my truck, however after running for about 10 minutes the cold air changes to warm or even hot air. I"ve tried washing out the radiator and condenser, topping off the anti-freeze, and cleaning the engine air cleaner and cab air cleaner. I had a service company look at it last year and they said the gas levels were within operating range so I"m wondering if either the gas has leaked out of the course of the year or if there is some other problem I need to take care of in order to keep the air cold. Thanks for any advice.

Just a thought--make sure that the belt that runs the compressor is tensioned right and that the a/c clutch is not slipping when the tractor warms up. Hope this helps.

make sure the heater valve isnt leaking. if both heater hoses are hot then it is leaking. this would make sense because the engine is cold in the morning and it warms the coolant up as it runs

It needs to have gauges attached to check the hi/lo pressures.

Air conditioning systems are built to "protect" themselves. Couple of points:

Just not familiar with your system, but with it being only four years old, I'd assume it uses an oriface tube.

Doubt if the freon is low; it would never get cold in the first place.

I'll just bet that oriface tube screen is about 95% plugged and the hi pressure is going thru the roof tripping the hi pressure switch open and shutting everything off.

Also, tractors are real bad about getting dirt in the evaporator core; they flat plug up with mud.

Need a set of guages on this bird to see what is happening. If the high side gets upwards of 350 lbs, something is plugged.

Secondly, if the system happens to use an expansion valve set up, the dude is freezing up and shutting itself down after a period of time.

Are you running that temp control all the way over on "max cold"? A good clean system ought to perform very well at "mimimun cold". At "max", the evaporator is never allowed to thaw itself and will just continue to build up ice around the core.

Let us know what you find,

Allan

Very likely low refrigerant regardless of observed low and high-side pressures.

I know nothing about your system - but a plugged orifice tube - or a plugged screen on your expansion valve can do it. So can too much air - or an overfill of system oil.

Often an AC system that blows cool at first and then gets warm has too much air in the system. Or . . . not enough refrigerant.

I've got one here that sort of defies reason - at least it defies my reason.

98 Dodge Grand Caravan. Just put a new compressor in it, evacuated for an hour at 29 inches, and then put in the exact OEM charge - i.e. 34 ounces. When done - it blew cold air when first started and then gradually got warmer the longer the engine ran. Did it every time I started it.

Checked all pressures against ambient temps and all checked perfect. I then went on to further checks - with a thermocoupler on the discharge line. When you compare line temps to low and high side pressures it is supposed to tell you if charge is too low or high. Again . . . all checked perfect.

So - I then brought it to an AC shop and the guy told me my orifice tube is plugged. Well . . . my system does NOT have an orifice tube - so I decided I did not trust the "expert." My system uses an expansion valve.

Went home - added two more 12 ounce cans of refrigerant - and it took off and now works pretty good. Drove 100 miles yesterday - 86 degrees outside and the AC blew 50 degrees F for the whole trip. Maybe not perfect - but good enough for now. I checked my Ford F250 and it blew 42 degrees F out the ducts - but it IS a different system and also uses R12 and not 134A.

If someone knows why my system works when 24 ounces overfull - I'd like to hear some ideas. But for now - I'm leaving well enough alone.
And by the way, the low and high side pressures barely changed with the added refrigerant.

I did wonder if some of my 10 year old cans of refrigerant were maybe, not full? So I weighed one full and empty. 15 ounces full and 3 ounces empty - so I guess that's not the problem.

jdemaris,

I dont' know much about your van but is it possible the OEM spec on refrigerant quantity is out to lunch? Do those vans have an auxillary evaporator in the back for the other passengers?? If so, that might answer for the seemingly high quantity of refridgerant needed??

Seems odd that the gauge readings were good with 34oz and still good with an additional 24oz but if the gauge readings are within spec. and you've got cold air, theoretically it shouldn't be overcharged................

No, mine doesn't have the optional rear AC system.

In regard to pressures - once a system is full the pressures won't change very much if you overfill. It just causes other problems.

I'm not an AC expert; nowhere close. I've been doing it for 40 years - but usually just know enough to keep my own stuff going.

This Dodge van threw me for a loop at first because it has computerized HVAC controls on the duct output blending doors. It also has a "cool down" computer check. It failed until I added the two extra cans and now it's passed and the warning lights have gone off.

Hello farmallfarmer.
Sounds like you may have an air flow problem.
If the ac charge was low it would not get cool as you say it does when it is first strated.
Your system probably has 134a as a refrigerant, and compared to the old R12 freon it carries a much higher high side pressure.Having gauge pressures readings would help on the diagnosis, when the unit is first started and when it failes to cool. If it was low on gas it would act the way you discribe,(I don't think so),Here are 2 of my guesses 1: Hot water is getting into the heater core see if you can feel the heater hoses.The old systems did not blend the heat into the evaporator, newer systems do so to controll cooling output. Heating output in BTU'S is about 3 times more than cooling BTU's. If the heater valve/controll is fully on the air conditioner will never catch up but If the system is fully charged it would be dumping water out of the drain like crazy.If you have the old type system the heater hoses should be warm to the touch not hot. I would run the unit until the cooling stoppes, and then blow air with a fan at the condenser and see if it makes a difference.There is many other resons for the unit to stop cooling including some of what the other posts suggested .
Just something easy for you to try.
Guido.

A question like this was on here a couple weeks ago and could be as simple as asking the right questions i.e. has there been a major component change on the system? If so was it done by an experienced A/C person? The reason I ask is if there was a compressor change done and a new filter dryer installed and the system evacutated if this wasn't done you could have moisture in the system which will cause the symptoms you descibe.