I have a 7610 cab tractor bout a 85 model.How much should the low side pressure be at the compressor?I don't know the brand because it's been painted over.It's been hot here in mo. and it would be nice to get the ac working better but don't want to put in too much freon.Oh,I'm assuming it's 134-a ?
freon pressure
- Thread starter jake123
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It should be r12 if it's an 85. That is unless it has been retrofitted. Google r12 and r134a fittings an look at the images. It's not too hard to retro it. And you'll want to because 12 is high dolla. If'n you can get it
hizoot
Gold Member
There isnt a magic pressure number...but needs to be slightly above freezing temp on the gauge.(once the cab has cooled down to low 70's)
There is a corresponding temperature chart on the guage for each refrigerant. To correctly charge it,there are alot more readings than just pressures...such as outdoor ambient,indoor (cab) ambient,line temps ,superheat,subcooling,etc....
superheat on lowside should be 12 degrees,subcooling on high side should be 3 degrees
..oh,btw...this is at 1500 rpm
There is a corresponding temperature chart on the guage for each refrigerant. To correctly charge it,there are alot more readings than just pressures...such as outdoor ambient,indoor (cab) ambient,line temps ,superheat,subcooling,etc....
superheat on lowside should be 12 degrees,subcooling on high side should be 3 degrees
..oh,btw...this is at 1500 rpm
Well I wish I could get the cab in the 70's lol I think i'll put my ac temp guage in the vent and try to lower the pressure first,notice temp and i can always add some more if it gets worse.I will keep it at 1500 rpm's also,thanks for the info.
Not so fast, your a/c gauge MUST have a 134 scale on it.
As for R-12, not is it only big bucks, you must be licensed and have a reclaiming station.
RickB
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That value is pretty much immaterial.
Tx Jim
New Member
I'm curious as to what the high pressure is. Ambient temp affects what the highest high psi an ac system should operate efficiently. When I check my AC systems I pay more attention to the high pressure gauge than the low pressure gauge to determine if system has correct amt of freon.
shaley
Platinum Member
I'd just add freon until the evap is cold with just the last tube flashing to vapor. About 10 deg superheat. Do you have a sight glass. You can't really tell freon level with gas pressures unless you have a charging chart for that particular system. Gas pressure is a function of its temperature.
RickB
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Maybe, maybe not. Have you ever seen a published specification for system static pressure?
the pressure is 90,engine off and 28 at 1500 rpm's, The temp is 58 in the vent.I only ran the motor for 10 minutes.At this pressure,curious if the evaporator would freeze up like it would it a vehicle.I guess I'll try and add more and watch the temp in the vent.I am like yes deere,been messing with adding,pulling vacuums,replacing expansion valves,orifice tubes,etc. Just kinda go by the seat of my pants. lol I did notice there was a good bit of oil that come out of the low fitting when i took off the guages.I know too much is not good.Maybe I should evacuate the system,pull vacuum and recharge?
i did wash the condenser lately,this makes a big difference.
Thanks for all the replies,definately different opinions lol
i did wash the condenser lately,this makes a big difference.
Thanks for all the replies,definately different opinions lol
RickB
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28 psi low side pressure isn't all that far off. 58 degree vent temp doesn't tell us anything without knowing the ambient temp. My rule of thumb for tractor A/C systems is if I can get a 30 degree differential between ambient and vent temps, that's usually pretty good. Make certain that the heater control is shutting off the flow of coolant to the heater core. Pinch a heater hose off with needle nose visegrips or a hose clamping tool and see if the vent temp drops further. When the heater fights with the A/C, the heater wins EVERY time.
Well,it was about 88 outside when I checked it.I heard about the 30 degrees difference,I agree with that when it comes to central units and window units,but with car ac's I like to see at least 40-50 degrees with temp difference.Usually you have a temp reading around 38-45 degrees at the vent.I shut off the heater valve weeks ago.Low pressure flucturates with the outside temp,so I try to compensate for that.I still think I need more than 28 lbs.on the low side but not for sure.It's the first time I messed with a tractor.
I think my major problem is with all the glass on the cab,It's so hard to cool.
Maybe I need some blinds inside to open and close lol
Thanks for the reply,this is getting interesting
Alan
I think my major problem is with all the glass on the cab,It's so hard to cool.
Maybe I need some blinds inside to open and close lol
Thanks for the reply,this is getting interesting
Alan
134a on any system is gonna run higher than 28 on an 88 degree day. Keep it at 1500 rpms and add some. Bleed the tank line(yellow) for at least two seconds. Then open it up. Keep a hand on the low side line and feel for the surges of cold. When there is no fluctuation in temp it's full. Doesn't need to be perfect just gd cold
