Thank you all so much, I have learned a lot. The system won't let me rep any of you...

I took a ten mile ride and it is blowing signficantly cooler now! Maybe it just took some time for the new refrigerant to circulate around and start doing its magic.

The compressor clutch is still not cycling off, though. So I will take a new pressure reading with doors open as Gary suggests. And then probably add another can as ri_truck_guy suggests. His advice makes more sense to me than the silly guage-on-a-can warning scale. No go boom.

What is the normal On/Off cycle time of the compressor clutch on a perfect system?

I'll also keep an eye on my compressor clutch to make sure it doesn't start slipping due to my slightly out-of spec hub/pulley air gap.

Thanks again, you guys have been a big help and I learned a lot.

 

Matt - Glad it is finally working better. If the clutch isn't cycling I'd bet you are still a tad low. These systems have a low pressure switch, meaning the clutch drops the compressor out if the pressure goes too low, and IIRC they have a high pressure switch. You should build up enough pressure to cycle the compressor to be fully efficient.

Having said that, I have no clue what the duty cycle should be, and I don't think there is a number for that. The pro's work off of pressure and temp - get it within the window and you are good to go, regardless of how long the compressor runs. But, obviously, it shouldn't drop out due to low pressure.

 

Great, makes sense. I *think* my compressor used to (last summer) cycle on and off quite regularly. In retrospect, I recall hearing that *click* sound periodically, which I NOW know is the sound of the clutch/hub closing the gap between it and the pully when the magnet comes on.

On another note, I think my TFI module is intermittantly failing. I have to crank for longer to start the truck when the engine is hot. And my vacuum gauge is not rock steady at 19 inches - it has an intermittant fluctuation to 18 inches at idle. I believe this twitch is caused by ignition misses. But that may be a topic for a different thread.

 

It's been my experience, on a really hot day the clutch will not cycle. With lots of warm air hitting the coil inside the dash, the pressure never lowers much, and it keeps it engaged. I only hear or feel the clutch cycle on a cooler day when the coil gets colder and the pressure goes lower. Or it will cycle a lot when the system gets low of freon.

 

Don't forget to spread some Di-Electric Grease on the back of the TFI Module when you replace it.

 

I'll use Arctic Silver thermal compound: Arctic Silver, Inc. - Thermal Compounds
Recomended by Rogue_Wulff and others.

And I'm going to remote mount it on a heat sink, with before and after module temperature readings: https://www.ford-trucks.com/forums/1...l#post12034545

Sorry to original poster and everyone else, I have totally hijacked this thread.

 

Galendor, what all is involved with the R134 conversion? As in, what new parts am I going to need to replace or add to my existing components?

 

I should have been more explicit: I paid a mechanic to convert mine 2 years ago. I had less confidence/knowledge back then. Now I think I would probably do it myself.

There are do-it-yourself converson kits you can buy, you can find these kits over by the R134 cans in most auto stores. I have read the back of these kits, and am therefore now an expert .

Basically there are some different o-rings and valve fittings in the kit that directly replace ones already present in the R12 system. What is required to do it right is that you try to remove any previous R12-type oil in the system by applying suction (via a vacuum pump) to one port and a safe cleaner to the other (ethanol is used). You suck some ethanol through the system, and keep a vaccum on it for a while to volitilize and remove any remaining ethanol and help dry out the system (you don't want water moisture in there). Then you fill the system up with R134 and the kind of oil that goes with that. Before filling, you should put a vacuum on the system and make sre it can hold a vacuum for 30 minutes or so (mine did hold vacuum for 30 minutes, I remember). If it cannot hold vacuum, there is a leak somewhere and no good reason to add the expensive refrigerant plus oil until that leak is found and resolved.

Others here such as Archion are experts and have written write-ups here on the conversion. They suggest other steps such as replacing the Accumulator/dryer (black cinnister) with a new one at this time, etc.

 

Here I go again; You can re-use the old r12 o-rings and lines, as long as they were the original ones already exposed to the r12. You can also leave the old r12 oil in the system, it doesn't mix with the 134a and it's new oil, so it just lays around here and there in the system doing nothing but taking up space.

As long as you pull a good vacuum on it and everything is tight, 9 times out of 10 you can put the 134a/oil mix in and it will work. Of course there are lots of circumstances that can happen with the system to require you to do more, but if it's in good shape, you can just pull a vacuum, stick it in, and go.

 

Dave is (of course) correct, far more correct than me on this matter. One can find a lot of conflicting information on the internet on this topic. But Dave has a built reputation for knowledge and helpfulness in automotive matters in general and our trucks in particular. Here's a short write-up I found on the web that supports what Dave said: Automotive Air Conditioning Conversion to R134a