Refilling A/C on a 90 sub w/ rear air

[blazerbones]

Hi all,

I just converted to r134a (flushed compressor with oil, lines/heat exchangers with solvent, new o-rings, orifice tube, expansion valve) and am refilling now.

I put 9oz of oil in the system and had it vacuumed. Held vacuum fine. Got it home and refilling (with cans).

I only got 24oz's in it before it showed full. Should be 70 plus oz's.

Something doesn't add up and wondering if anyone had any ideas???

 

[Fordum]

Not real sure what you mean by full. Unless you have a sight glass, there is no full mark.
If you are going by pressure, which side are you looking at? If the high side is too high, check the cooling fan to be sure its moving enough air. Or else your accumulator/dryer is stopped up.

If the low side is too high, then something is wrong with the orifice tube you put in, or the expansion valve.
BTW, I don't know of many that use both.

Also, you do know that the engine has to be running to put the gas in, right?
Sounds like you just got in what the vacuum in the system would draw in.

BTW, if you did not know that, DO NOT charge into the high side with the engine running.
In other words, if you did not know you have to have the engine running. STOP, and tell us and we can talk you through the correct hookup.
I know this sounds condescending, but I saw a guy blow up one of those cans by hooking it to the high side, and better safe than sorry.

J.

 

[blazerbones]

I hear that. I do know how to hookup. Charge from low side with engine running and AC on max cool. Jumper the pressure cutoff switch if you are too low on charge for it to work.

I did add another 2 cans... that makes 48oz's of 134a... I was just expecting 70 or more... that's 80% of the R12 capacity.

The rear evap is controlled by expansion valve, the front an orifice tube. Both are new and dryer/accumulator too.

The pressure shows 45psi on low side running at 75degrees outside and the high side shows 200. The compressor clutch does not cycle, just stays engaged. The air is pretty cool.

If the condenser is underperforming could that be the reason for higher pressures at lower than capacity charge?

I could just call it good and enjoy the cold air, but I want to screw up as little as possible.

Thanks for all the help!

 

[Fordum]

Great, I have seen one of those cans turn into what looked like a softball from the pressure, and saw the results after one exploded.
Not pretty.
134 runs at higher highside pressures than 12. Without my gauges in front of me, I could not tell you how much.
I don't do enough ac work anymore to remember the actual pressures, but I know the needle positions when I see them. <G>.

Someone here should be able to chip in the actual pressures.
Also 134 often needs a bigger condenser to perform properly. That is the biggest cause for the complaint about 134 not being as cold as 12.
A system that is designed for 134 is, if anything, colder than 12. But you have to get rid of the heat.
A friend of mine who does lots of conversions in his shop has a source of supply for condensers that have more tubes, or are bigger. Not sure where he gets them.
And after I wrote the first reply, I realized that you probable had a two part system and that is why you had both types of metering gadgets.
Sorry about that.
With that two part system, you might be looking at a bigger condenser. Might find one in a junkyard. Caddies seem to have big ones. Don't know how much trouble it would be to fit it though.

J.

 

[blazerbones]

My dual elec fans are helping out the condenser some!

I have read that the newer condensers are all parallel flow, thus perform better. Going that route would be a big upgrade. Not sure where to get one that fits.

I got it dialed in I guess. With the AC on med fan speed front only, the compressor cycles every minute or so.

On High both front and back... the compressor don't stop... I don't think I should remove any of the charge as it is substantially less than recommended amount.

It's never easy it seems.

 

[4xcrazy]

a buddy of mine just did the AC in his and another friends truck, same setup with the front and rear AC units.

You HAVE to have the rear AC fan on high as well, to get the expansion valve to open and let freon pass through it as well.

his pressures were around the 45-50 range or so on the low side, but were up near the 250-270 range on the high.

These were normal pressures for most systems i have also been told by an old boss at work that used to run an auto repair shop.

the compressor doesn't really have to cycle, as long as the pressures stay constant, or where they need to be, it'll be fine.

if you are still running the old condensor that was for the R-12 freon, you may need to run another electric fan on the front of it, otherwise your AC will only really be "real" cold at higher driving speeds.

i will argue this till i'm blue in the face with anybody that says their AC "works just fine"

ok fine then, put a 134 condensor on it and see just how much better it gets, is what i tell them

 

[4xcrazy]

I have read that the newer condensers are all parallel flow, thus perform better. Going that route would be a big upgrade. Not sure where to get one that fits..

as far as i have seen, all the aftermarket units that are called for these trucks are 134 condensors, i asked this question when i bought my new one. i think i paid like $130 for it too or something like that, it wasn't too horrible of a price.

i have yet to find out just how well it works, because as i was putting the freon in, the seals on the compressor decided to blow out.

 

[bigblock72]

Hi all,

I just converted to r134a (flushed compressor with oil, lines/heat exchangers with solvent, new o-rings, orifice tube, expansion valve) and am refilling now.

I put 9oz of oil in the system and had it vacuumed. Held vacuum fine. Got it home and refilling (with cans).

I only got 24oz's in it before it showed full. Should be 70 plus oz's.

Something doesn't add up and wondering if anyone had any ideas???

Did you get all of the flushing solvent out? Any amount of flushing solvent will cause the pressures to be high. With the system only taking 48 oz I'd bet there is some flushing solvent still in the system.

If it's getting cold enough for you and the high side pressure stays below 300 psi then I'd just leave it alone for now.

 

[blazerbones]

Did you get all of the flushing solvent out? Any amount of flushing solvent will cause the pressures to be high.

I was VERY worried about that when flushing the system, so I took great care. I do not think there was ANY flushing solvent. Just 9oz of oil (ester 100).

I also had a vacuum on it for 30 minutes with good result.

Good suggestion though, I'll guess I'll find out sooner or later.

 

[blazerbones]

as far as i have seen, all the aftermarket units that are called for these trucks are 134 condensors, i asked this question when i bought my new one. i think i paid like $130 for it too or something like that, it wasn't too horrible of a price.

Good to know!

I cleaned up the old condenser (flush, no bugs/bends, etc) and the evaporators. I will replace the condenser when I replace the compressor.... hopefully in 8 years or so!

I do understand that the system condenser is not designed for r134a. The very large specific heat (ability to carry large amounts of heat without large change in temperature) of r134a demands the parallel flow design.

Total cost of this was like $200 WITH 2 weld repairs on the rear evaporator that wuz leaky.