So today I'm going to order the parts to fix my A/C in the Grand Am. I have quite a few selections on orifice tubes it seems. Is there any performance over an automatic adjusting orifice tube compared to the standard fixed orifice tube? Well besides the $17 anyways.
Orifice tube selection help
- Thread starter SEMI_287
- Start date
- Status
I would stick with the original style fixed orifice. They work plenty good and their simplisticy and reliability is their main point. They almost never go bad and if you inspect it and the screen is fairly clear and intact, I'd just reuse it.
Originally Posted By: mechanicx
I would stick with the original style fixed orifice. They work plenty good and their simplisticy and reliability is their main point. They almost never go bad and if you inspect it and the screen is fairly clear and intact, I'd just reuse it.
I agree! The only negative to reusing the orifice tube is that most often it has to be replaced to support new replacement parts warranty.
I would stick with the original style fixed orifice. They work plenty good and their simplisticy and reliability is their main point. They almost never go bad and if you inspect it and the screen is fairly clear and intact, I'd just reuse it.
I agree! The only negative to reusing the orifice tube is that most often it has to be replaced to support new replacement parts warranty.
Originally Posted By: mechanicx
I would stick with the original style fixed orifice. They work plenty good and their simplisticy and reliability is their main point. They almost never go bad and if you inspect it and the screen is fairly clear and intact, I'd just reuse it.
Do this.^
No one can predict how that particular variable orifice valve will work in your car.
However, different orifice sizes DO make a difference in biasing the system for different operating conditions.
Stock is safe and usually a good compromise.
I would stick with the original style fixed orifice. They work plenty good and their simplisticy and reliability is their main point. They almost never go bad and if you inspect it and the screen is fairly clear and intact, I'd just reuse it.
Do this.^
No one can predict how that particular variable orifice valve will work in your car.
However, different orifice sizes DO make a difference in biasing the system for different operating conditions.
Stock is safe and usually a good compromise.
Thanks guys, I'll save the $17.
Originally Posted By: mechtech2
No one can predict how that particular variable orifice valve will work in your car.
However, different orifice sizes DO make a difference in biasing the system for different operating conditions.
Stock is safe and usually a good compromise.
All the advice to "use the stock fixed type" is indeed a safe and predictable choice. I just don't like compromise ;-) Every automotive AC system I've owned which is orifice-tube based is inferior at low speed to every automotive AC system I've owned which had an expansion valve. And a "variable orifice tube" is just an expansion valve that cues solely off differential pressure instead of pressure combined with temperature (and some "smart" VOV's use temp as well, and really are functionally equivalent to TXVs). That's the problem with a fixed orifice- at low compressor speed it can't maintain enough pressure differential to efficiently boil refrigerant in the evaporator and condense it in the condenser, so a percentage of the refrigerant just circulates as gas, doing nothing useful.
No one can predict how that particular variable orifice valve will work in your car.
However, different orifice sizes DO make a difference in biasing the system for different operating conditions.
Stock is safe and usually a good compromise.
All the advice to "use the stock fixed type" is indeed a safe and predictable choice. I just don't like compromise ;-) Every automotive AC system I've owned which is orifice-tube based is inferior at low speed to every automotive AC system I've owned which had an expansion valve. And a "variable orifice tube" is just an expansion valve that cues solely off differential pressure instead of pressure combined with temperature (and some "smart" VOV's use temp as well, and really are functionally equivalent to TXVs). That's the problem with a fixed orifice- at low compressor speed it can't maintain enough pressure differential to efficiently boil refrigerant in the evaporator and condense it in the condenser, so a percentage of the refrigerant just circulates as gas, doing nothing useful.
I don't think aftermarket variable orifice tubes work that well or like a dedicated TXV. I don't think GM's Variable Displacement Orifice Tube A/C system gives up any performance or has an issue with keeping the low side low enough. I think with the accumulator on the low side (which allows for "overfilling" of the evaporator)combined with VDOT's control valve, or even a cycling clutch for that matter, works well.
The main thing here is GM's variable displacement compressor and control valve control the pressure and a variable orifice tube or TXV is not necessary.
In theory a TXV might work better at times but there are ways to compensate. I wouldn't tinker with what is an effective almost foolproof design.
The main thing here is GM's variable displacement compressor and control valve control the pressure and a variable orifice tube or TXV is not necessary.
In theory a TXV might work better at times but there are ways to compensate. I wouldn't tinker with what is an effective almost foolproof design.
I have about 100 Variable Tubes I'll give you. We had so much trouble with em that we stopped using them.
Well, y'all have more experience with VOV's than I do, so I'll gladly defer. And cross it off my list to try if one of the Jeeps needs one... ;-)
As for the accumulator allowing for overfilling... a high-side "receiver/dryer" actually allows for more system capacity because, sitting on the high-side downstream of the condensor as it does, it holds liquified refrigerant. The low-side accumulator only holds gas and froth (its really just a trap to catch any liquid that gets spluttered out of the evaporator). Liquid is far more molecules of refrigerant than an equivalent volume of gas. One of my beefs with the Jeeps is that they have accumulator systems, and they ride a knife-edge of being over versus underfilled compared to, say, the 93 Eagle we had which still used a receiver/drier. The EPA likes accumulators because less refrigerant is manufactured and sold to fill that type system.
As for the accumulator allowing for overfilling... a high-side "receiver/dryer" actually allows for more system capacity because, sitting on the high-side downstream of the condensor as it does, it holds liquified refrigerant. The low-side accumulator only holds gas and froth (its really just a trap to catch any liquid that gets spluttered out of the evaporator). Liquid is far more molecules of refrigerant than an equivalent volume of gas. One of my beefs with the Jeeps is that they have accumulator systems, and they ride a knife-edge of being over versus underfilled compared to, say, the 93 Eagle we had which still used a receiver/drier. The EPA likes accumulators because less refrigerant is manufactured and sold to fill that type system.
I think the real problem with later model A/C systems is they are using less refrigerant regardless if they have the TXV and a receiver drier or not. GM use to put over 3 lbs of R12 in their OT systems with accumulators, so I don't think the OT with accumulator system really limits refrigerant capacity. Some of the new systems with even the TXV and receiver driers have less than a pound of 134a. It doesn't help that they also often use a cycling clutch whereas I think the VD compressor control valve performs better.
The OP system if it is a Grand Am has VDOT and 1.75lbs of refrigerant iirc. I think they outperform a lot of later model TXV w/ receiver driers and don't need tinkering with.
The OP system if it is a Grand Am has VDOT and 1.75lbs of refrigerant iirc. I think they outperform a lot of later model TXV w/ receiver driers and don't need tinkering with.
Another issue with low AC performance at low speed is that most people never think to check for correct fan clutch operation on a vehicle that uses this. A lot of fan clutches never get replaced. As far as vehicles that only use electric fans, it depends on the design and how many fans are being used.
Some AC systems just are poorly designed and will not run very well at low speeds.
All of my current vehicles use a fixed OT and I have no problem with AC performance, even at low speeds.
Wayne
Some AC systems just are poorly designed and will not run very well at low speeds.
All of my current vehicles use a fixed OT and I have no problem with AC performance, even at low speeds.
Wayne
most 134a systems seem to like being underfilled a bit. Our trucks run very cold with far less than spec amounts of refrigerant.
And fan clutch (if present) is critical in Florida, I can often tell when one is going south by the drop off in ac performance at low engine speeds.
And fan clutch (if present) is critical in Florida, I can often tell when one is going south by the drop off in ac performance at low engine speeds.
Originally Posted By: SteveSRT8
most 134a systems seem to like being underfilled a bit. Our trucks run very cold with far less than spec amounts of refrigerant.
Agreed completely, and IMO this is another reason that so many of today's accumulator systems with a small total charge really ride on a knife-edge. They go from slightly underfilled and performing GREAT, to just plain underfilled and hardly cooling at all with a very small loss of refrigerant. My Jeeps and the PT Cruiser are prime examples of this- the PT is now 7 years old and my wife said that the AC wasn't cooling well this spring. I gave it a check, and the pressures were just barely below spec... about 1/8 of a pound brought it right back to normal. When the 99 Jeep had a leaky evaporator it was the same way, but every couple of months rather than every 7 years
A new evaporator core fixed that, but also drained my wallet because of the total dash removal required to install it. I'm too old and lazy to do that shtuff myself anymore... I'll still remove an engine, but interior and under-dash work while standing on my head just makes me mad. ;-p
I've retrofitted my two old rides with R-134a (total conversion with hard-line, evaporator, and condensor flushing, new rubber hoses etc.- not a hack job "conversion in a can.") They both retained their large receiver/driers and took a very big charge, even at the conversion rate of 80% by weight R-134a relative to the specified R-12 charge. Both have been working great for years now, and I think that's because the receiver/drier system is so forgiving in terms of charge. I *know* that the '69 must leak some refrigerant because it has its original RV-2 compressor still in there (the '66 has a modern Sanden). At their best when new and using R-12 and mineral oil, those RV-2 compressors were slightly leaky beasts with 2 head gaskets, 2 valve plate gaskets, an oil pump access plate gasket on the back, carbon front shaft seal, front bearing housing O-ring, and oil pan gasket all available to slowly weep refrigerant. But it still cools great and I haven't put an ounce in it since I converted it in about 2004.
most 134a systems seem to like being underfilled a bit. Our trucks run very cold with far less than spec amounts of refrigerant.
Agreed completely, and IMO this is another reason that so many of today's accumulator systems with a small total charge really ride on a knife-edge. They go from slightly underfilled and performing GREAT, to just plain underfilled and hardly cooling at all with a very small loss of refrigerant. My Jeeps and the PT Cruiser are prime examples of this- the PT is now 7 years old and my wife said that the AC wasn't cooling well this spring. I gave it a check, and the pressures were just barely below spec... about 1/8 of a pound brought it right back to normal. When the 99 Jeep had a leaky evaporator it was the same way, but every couple of months rather than every 7 years
A new evaporator core fixed that, but also drained my wallet because of the total dash removal required to install it. I'm too old and lazy to do that shtuff myself anymore... I'll still remove an engine, but interior and under-dash work while standing on my head just makes me mad. ;-pI've retrofitted my two old rides with R-134a (total conversion with hard-line, evaporator, and condensor flushing, new rubber hoses etc.- not a hack job "conversion in a can.") They both retained their large receiver/driers and took a very big charge, even at the conversion rate of 80% by weight R-134a relative to the specified R-12 charge. Both have been working great for years now, and I think that's because the receiver/drier system is so forgiving in terms of charge. I *know* that the '69 must leak some refrigerant because it has its original RV-2 compressor still in there (the '66 has a modern Sanden). At their best when new and using R-12 and mineral oil, those RV-2 compressors were slightly leaky beasts with 2 head gaskets, 2 valve plate gaskets, an oil pump access plate gasket on the back, carbon front shaft seal, front bearing housing O-ring, and oil pan gasket all available to slowly weep refrigerant. But it still cools great and I haven't put an ounce in it since I converted it in about 2004.
Like I said, orifice tubes in auto AC systems are biased.
But if we make it better at low flow, then what about the loss at cruising speed? And visa versa?
But if we make it better at low flow, then what about the loss at cruising speed? And visa versa?
- Status
