Well, today I pulled into Plant Equipment Company (PECO), yanked my A/C hose (he he) and walked it in. They replaced the damaged hose with Aeroquip while I waited, and charged me only $13 bucks + tax. Then I went home and replaced the expansion valve with the one for the non-intercooled truck (it's the only one I could get), made a pigtail to clear the A/C motor housing and put it all back together. Then I pulled a vacuum for 20 minutes. Then I started to add R134a. After only 1/2 a can, the A/C line going into the H-valve got cold. I finished the can and the outlet temp in the truck felt pretty cold. The sight glass was still bubbly, but I decided to stop there and test (note the recommended is three cans). I went for a drive with my temp monitor in one of the ducts, and the temp went down to 31.9 degrees at one point! It never went above 38 deg the whole trip. This is colder than my A/C has ever been the whole time I have owned the truck. I have even had the "pro's" work on it, sucking it down for an hour and all, still it's never gotten down into the 30's.

Conclusion: I think R134a works best with WAAAY less head pressure than R12. Either that or my truck is possessed, which I have a strong suspicion of...

 

What are the pressures reading?

 

About 38 on the suction side, and 150 to 190 on the pressure side.

 

That's a little low for 90 degree weather.

I am running 2 cans of 134a.

 

It's not 90deg right now, it's low 80's, maybe that's why the pressure is low.

 

Nah, it's because it needs more refrigerant. With only half a can I'm surprised it's not cutting in and out.

 

It has a whole can, plus about 5 seconds of the second. It's not cycling much.

 

I had that in the original post (the one can thing).
I wonder if it's an altitude thing. Water boils at a much lower temp up here than sea level (Bernoulli's law) so maybe I need less freon.....

 

I have to haul 2 tons or gravel tomorrow, can't wait to freeze my face off (if the A/C still works in the morning)!

 

i had to pull the cycle switch tube out of the suction line about 2 ins. on my 90 to get the cycling to work right. the only diff. i see in the 2 is it takes 134 about a mile farther to take a really hot cab temp down to the comfort zone.

 

My "one can" A/C bomb is working better than I could ever expected. It was in the 90's yesterday when I went into Albuquerque to rescue my Wife with a bad starter, and on my way home it started to rain. My temp proble showed 24.8 degrees, and I could see my breath! It was perfect for me.

I can't believe all these years even the professionals had it wrong on the A/C charge with 134a. As I said before, I never had good A/C in this truck or my brothers 1993 Gasser W250, and I had it professionally worked on by two different shops over the years mixed in with my own feeble attempts to make it better.

Now it's better than any A/C I have ever had, save for my 1969 Plymouth Fury with that Harley engine for a compressor!

 

when i charge with 134 i fasten a thermo on the suction line. sdd gas and watch temp. note coldest temp. add gas until it starts rising and it will. remove gas back to lowest temp. that is as cold as the unit is going to go.

 

That's what I did also except I used the less accurate "thermometer of the hand" technique!
I like your idea better!

 

You need to add some R134a compatible oil too.


M

 

Since you also changed the expansion valve could this be most of the differance in cooling? I would be interested to know if you put a full fill in, would it change.

I finally have mine working good, turned out to be a bad expansion valve. Did not play with fill level, just filled to factory specs.