Is the Cycling Clutch Orifice Tube(CCOT) AC system a more reliable/better performing system than its predecessor, the Thermostatic Expansion Valve(TXV) system.

I am in the process of installing a salvaged 1978 TXV unit in a 1979 F100. Have mounted the blower/evaporator/duct assembly. Ordered a parallel flow condenser to replace the stock tube and fin condenser. Will fabricate new hoses as required.
Will be using 134a refridgerant.

Should I replace the TXV/receiver drier, keeping the original design OR convert to a variable orifice tube/accumulator drier/cycling clutch system?

The main reason I am posing this question is that I don't know whether a replacement TXV will be set up for R12(as was used in '78). If I modified the system I am installing to a CCOT, I could use a cycling switch mounted in the accumulator drier that that is designed to work with 134a(21psi).

 

That's FFOT (Ford Fixed Orifice Tube) around here, please! CCOT is the General Motors name.

A properly running R-12 FFOT will cool just as well as a TXV, and vice-versa.

I think the real driver for the change to FFOT from TXV and POA and STV systems was to improve fuel economy, by reducing compressor run time via cycling. The FFOT will cycle in all but the highest heat/humidity conditions.

I would expect that replacement parts for a R-12 system would be R-12 compatible only, unless specified otherwise. I really wonder whether you would find a Ford TXV that was HFC-134a compatible.

I think if I was building a 134a system from scratch, I would go FFOT, and use the 134a compatible parts that are available. For instance, an Accumulator that has XH7 or XH9 dessicant in it, as they are compatible with 134a (and supposedly backward compatible with R-12, too). And get a 134a compatible Cycling Pressure Switch. If I was doing it, I would just use my '94 Bronco as the example to look up 134a compatible parts, as it was 134a from the factory. That Orifice Tube could be used (inserted into the Evaporator inlet tube), or you can get an external splice-in type of Orifice Tube holder.

Then there are those who say that the Variable-Orifice Tube thingy replacement for the Fixed Orifice Tube works good for 134a in particular. I have not tried one, so I can't say it does or it doesn't. Supposedly, it would improve cooling at low engine RPM, like when idling, as compared to the Fixed Tube.

Use Green O-rings only.

 

Torky2, thanks for the detailed reply and for the heads up on the FFOT terminology.

I'll be installing thoroughly cleaned or new components without residual mineral oil lubricant. Is PAG oil the preferred lubricant for R134a? If so, what viscosity?

Also, every Ford I have owned with an R12 era AC system has leaked from the garter spring coupling on the high side flexible line. I have read recommendations on using Nylog lubricant/sealant on green O-rings to minimize this problem.

Is there an improved design in couplings on newer systems that controls the leak problem?

 

My observations on the 2 O-ring garter spring coupling is that it tended to leak over time where it was subject to flexing. Like the connections to/from the Condenser. The engine would torque over, flexing the couplings as the Condenser is on the body and fixed. Had a recurring problem car with leaks there. Used new O-rings, coated them with Nylog (really stringy stuff!), and after putting them together, put on immobilizers. The immobilizer thing is a black chunk of plastic that holds both sides of the connection fixed, and tightens down with an Allen head screw that goes in tangentially. With it on, you do not re-use the old safety clip. It works great, 4 years later has not leaked R-12 at all. And that is in a high-A/C use climate.

I got the immobilizers from acsource.com I think. I don't think they sell car A/C parts anymore, just A/C tools. But I haven't checked their website for a long time.

Supposedly, Ford changed to a new coupling design that is longer and has 3 O-rings, all to reduce the lever effect of flexing unloading an O-ring. I haven't had one of those apart to see it myself first hand. Maybe because they are working and staying sealed!?!