Do I have an orifice tube on my rig and if I do where?Thanks

 

I'm sure you do. Locate the evaporator (the big box under the hood on the passenger firewall). Look for the input side, it is the tube going to the bottom of the evaporator, it goes down at an angle. This tube is part of the evaporator itself. In that tube is the orifice, pressed down into the wider top section of the tube. You can't actually see the orifice itself until the hose is disconnected.

 

The real question is: why are you looking for it? A/C systems are not all that complicated, but they present numerous opportunities for costly mistakes, and can be dangerous to work on to the uninitiated.

 

I will give you a hint,R134a conversion.

 

I would not claim to be a genius, but I am in fact ASE certified in AC systems, amoung other areas. I will now give you a hint.

For the conversion you are speaking of I shall assume that the system was fully functional and leak free at the outset ('88 ford, I doubt it). The R12 (it is still R12 isn't it) would have to be first identified and then recovered using the appropriate recovery/recycling equipment, as releasing it into the atmosphere is an illegal and morally reprehensible act. Each connection in the system would then have to be disassembled, including the one going into the evaporator case where the oriface tube is hidden. The evaporator, condensor and hard lines would then need flushed with an AC flush tool and specific AC flush solvent to remove all of the old Ester lubricant. The accumulator would need removed and discarded as it contains a dissicant and cannot be flushed. A proper conversion would include a compressor replacement using a unit that has seals that are made of the proper flouropolymer to resist breakdown caused by the R134a ('88 ford compressor is on its last legs anyways). A wise man would also replace all of the rubber hoses in the system, they are 15 years old after all. A new oriface tube would be installed in the aformentioned location. The proper quantity of PAG oil would be placed in all of the various components. The new accumulator would be installed. Each connection would receive the new flouropolymer o-rings and new garter-springs so common to Fords (too cheap to risk reusing). Assuming you have already installed the proper R134a conversion port fittings, you should double check your work, or maybe triple check as the case may be. Now your R134a gauge/manifold set can be attached, your vacuum pump connected and turned on. 30 minutes after the system has reached 30 in. of vacuum any flush solvent, moisture and most of the air that is in the system will be gone. Shut the valves off in your gauge set and let sit for 20-30 minutes. Did it hold a vacuum? If not go back and figure out why. If it won't hold a vacuum it sure won't hold the 250psi of high side pressure it will see. If all is well now you can add the OEM quantity less 10% of R134a to the LOW SIDE (lets not blow yourself up now!!) You realize it will be difficult to get that in there without the engine and system running to move some of that refridgerant to the high side. Of course you also realize that you will not likely have enough pressure to close the low side pressure switch and engage the compressor clutch right off. That's OK you thought to jumper the electrical connector on that switch to close the circuit temporarily. Now that you have filled the system you will verify both the high & low side pressures are correct for an R134a system and plug the pressure switch back in. You carefully disconnected your gauge set and checked your new fittings for leaks. Last but not least you should check to see that the system blows cold!!

I have one more special hint, one I save for my "friends". Your better aftermarket part stores (not walmart) have a relatively new variable oriface tube that changes the oriface size dependant on system demands much like an expansion valve in foreign car systems. It helps the system cool at low RPM. Try it, you'll like it.

 

I would suggest a brief review of the forum rules

"2. Be Courteous and Respectful - Ford Truck Enthusiasts is a Family Friendly web site."


"2.3 Do not post any material or comment that is badgering, heckling,
antagonistic or considered to be "baiting" others into an
unproductive conflict."

Everybody misreads a post sooner or later but let's keep it civil please.

 

lol

 

A few questions based on Okie Dax's reply:

What viscosity of PAG oil should be used in Ford AC systems converted to 134a? I'm installing components removed from a '78 Bronco on a '79 F100.

Will a new receiver/drier contain a dessicant compatible with 134a?

The '78 system uses a thermostatic expansion valve designed for use with R12. Is it possibe to buy an expansion valve with flow characteristics suitable for 134a?

How can you tell that a replacement compressor is 134a compatible?

The components available from my NAPA store do not state whether they are for R12, R134a, or both.

 

alanvng,

First, welcome.

PAG that is purchased from an auto parts store is purpose built for R134a a/c systems. I have not seen viscosity listed as a spec before. Any PAG should do, though I prefer name brands, I use Castrol.

Any new accumulator/drier manufactured in the last 10 years should be compatable with R134a, as it has been the standard during that time. Note that it has been against federal law to manufacture or import R12 since 1996. Any legally available R12 is either recycled are has been stored since then.

I would be surprised to find a thermostatic expansion valve on a 1978 Ford. I am fairly certain that that system used a fixed oriface tube and clutch cycling control. A good auto parts store should be able to provide you with the proper O tube for the conversion. I would recommend the variable tube that is now available for better cooling at idle.

Any compressor manufactured/remanufactured in the last 10 years should be labled as compatable. The parts store should confirm this for you prior to purchase.