Got a couple of questions for you AC guys.

Last night I charged the AC system on my 68 Val. I had rebuilt the compressor with all new seals, installed a parallel flow condenser, replaced all the system o-rings, installed a new rec/dryer and had all new barrier hoses made up for the rubber portions of the lines.

The system is now a 134a system. The old R12 system called for 2 lbs, 14oz of refrigerant. I have only put 2 lbs of 134 in the system thus far. And I have a MUCH larger system volume now with the upgraded condenser and a suction line that is more than 5X the length of the original line.

Unfortunately the new rec/dryer does not have a sight glass. So I can't see if things are foaming up. I thought I'd have to put a lot more refrigerant than the 2 lbs I have in there so far. But I don't want to go too far either.

Here are my #'s so far:

Idling at about 1200
80* outside temp
45* at ac discharge vent in car
25 lbs low side pressure reading
200-210 high side reading

Idle down to about 800
80* outside temp
50*-54* at ac discharge vent
30-40 lbs low side reading
250 lbs high side reading

This is all with the car stationary of course. No "ram air" through condenser, so I assume it will work even better when driving at speed.

If the temps are good should I just let it be? How can I tell when there is enough of a charge without the sight glass? Chrysler said in the fsm, once the sight glass had cleared to add 2-4 more oz. of refrigerant based on which condenser was used in the car.

I thought I'd be putting at least 3 lbs in the thing with the extra system volume.

Any thoughts from you guys would be greatly appreciated.

Cheers,

CE

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-76 Cordoba, 360 4bbl
-68 Valiant, 273 2bbl
-67 Dart /6 4bbl, Leaning Tower of Power!!!

That is a long suction hose!

Myself I prefer both hoses to come off on the same side like you have yours. It will be real easy to flip the compressor out of the way to remove the engine without having to open the system.

I suspect the volume of the new condenser is actually less than the old r12 unit that was replaced. Some of them have tiny passages. I can't really tell which style you have. I have a new 6mm tube condenser that is larger than my old one and I am sure it has less volume, probably quite a bit less.

The system will not need as much r134 as it would r12. I think you are close, but could use a little more. I would not expect it to need more than another half pound, and most likely less. The extra volume in that long hose is not that much of a factor since it is full of vapor not liquid.

I agree with what AnotherSix says; I think you're very close to having a correct charge. Bummer about no sight glass; they're very useful.

What kind of cooling fan is on this engine? What kind of expansion valve are you using?

(And, as a matter of interest, tell us more about the new hoses. You had a new fitting put on the firewall end of the low-side hose, then a new extra-long hose made up to mate to it...?)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The size of the suction hose will have very little effect on system capacity. The size of components on the liquid side will have the major effect. On R-134a systems, do not use a sight glass to determine the ammount of charge, it is not an accurate indicator. Most R-134a conversions will require approx 80% (this does vary) of the R-12 charge. The best way to charge a R-134a system of unknown capacity, is as follows.
Set up vehicle with a fan in front of the radiator/condenser, doors/windows open, A/C set on normal cool (outside air) high blower, hood open, engine rpm approx 1200-1500 rpm, good thermometer in the center A/C air outlet. Start with an initial charge of about 1/2 of the required r-12 amount. Let the system stabalize, and measure temp. Keep adding 134 in 2 oz increments and check outlet temp after allowing system to stablize, after adding the 134a. The temp should decrease each time. When the temp stops decreasing, the charge is correct. If the temp increases, you added too much. While doing this, watch the high side pressure. Do not let it go over 275 lbs. Did you add a high and low side pressure switch?

Actually your numbers look pretty good. Do you have a fan shroud?

PS: With a R-134a system it is better to be a little under charged then a little over charged. 4 oz over charge will result in a higher vent temp, then 4 oz under charge.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

not on a R-134a system. many R-134a systems will show bubbles with a correct charge. This it the main reason they were eliminated from most R134a systems.


Making up new hoses is no big deal, most any A/C shop can do this. I have the tools, and keep fittings in stock.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

Unfortunately I never hear that statement anywhere but in the garage ................

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-76 Cordoba, 360 4bbl

-68 Valiant, 273 2bbl

-67 Dart /6 4bbl, Leaning Tower of Power!!!

The cooling fan is the original fan. It is a ridgid type (not thermostatic anway) and as the car is a factory a/c car, I'm sure it is whatever plymouth was using back then.

The expansion valve is the stock piece.

The low side fitting at the fire wall is also a stock piece. I just cut off the original ferrule and put a #12 beadlock fitting on in place of it.

In fact the only non-stock fittings are 2 90* #6 beadlock fittings I used for the liquid line at the condensor, to the steel line that goes into the rec / dryer.

_________________
-76 Cordoba, 360 4bbl

-68 Valiant, 273 2bbl

-67 Dart /6 4bbl, Leaning Tower of Power!!!

Charlie,

Thank you for this. it is exactly what I needed.

Yes I am running a fan shroud. It took some work to get it mated to the radiator correctly as I had another row added to the rad when it was rebuilt last year.

The shroud now fits like it came from the factory, except across the top edge where it runs along the top tank of the rad. The top tank on the rad was set back to make room for the extra row, and there is now a gap there. I've been thinking of a couple of ways to handle it.

I did add a low pressure cut off switch to the rec / dryer. The original dryer didn't have one at all. I have yet to wire it into the lead to the conpressor.

I do not have a high pressure switch. Will the high pressure relief valve not take care of any problems in that respect?

Thanks again!!!

CE

_________________
-76 Cordoba, 360 4bbl

-68 Valiant, 273 2bbl

-67 Dart /6 4bbl, Leaning Tower of Power!!!

I know a sight glass isn't a perfectly good SOC indicator on a 134a system, but I still like to have a window to peer into the system and see what's flowing on the high side...even if all it'll tell me is "frothy foam", "a lot of bubbles", "a few bubbles", or other such generalities. Even better than that is a Dry-Eye, which'll also tattle on moisture in the system.

How many blades are on your cooling fan? Usually six or seven on the A/C equipped cars. Good work upgrading the radiator. The gap-sealing idea is a good one; ideally there'd be no gaps at the edges of the condenser-radiator-fan "sandwich" of parts. Keep an eye on the engine temp under high demand conditions (hot days/slow speeds/stuck in traffic).

Hate to say it, since you've already got the system sealed and charged, but adding a high-pressure cutout is somewhere between "a really, really good idea" and "mandatory" when going to an R134a. You don't want to rely on a high-pressure blowofff valve for anything short of a totally catastrophic situation.

Charrlie, what's your current thinking on TXV swaps (or non-swaps) when going to R134a?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Pretty sure it is a 7 bladed fan.

Figures on the high pressure sw!!

Maybe not a big deal though. I saw a combination switch that does both low and high pressure cut out. If I could get one that would fit into the spot on the rec /dryer where the low pressure switch is now, it would just be a simple bleed the system down, evacuate and recharge. No big deal.

I'll have to call the a/c supply place and see if that'll work!

Thanks,

CE

_________________
-76 Cordoba, 360 4bbl

-68 Valiant, 273 2bbl

-67 Dart /6 4bbl, Leaning Tower of Power!!!

Yup, a binary switch (High + Low cutout in one) will work just fine.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

A high pressure cut out switch is actually a legally mandated requirement (in the USA) on retrofitted A/C systems. I would do it any way to protect the system. Depending on the drier (OEM/aftermarket) you might or might not have to discharge the system to install the switch. If the switch port on the drier is female threaded, you must discharge the system, if the port has male threads, it most likely has a shreader valve in it, and discharge is not required. I would use a binary switch.

Dan
As for a sight glass, I'm with you. I like it as an "indicator", but the person working on the system must know what the are doing. Too many DIYer's would be geting trouble, using a sight glass and over charging the system. With the "charge kits" sold in the stores, that just have a hose and no gauge, people would try to charge to a clear glass and have the pressures out of site.

You know any time a A/C system doesn't get cold enough, the solution is to add refrigerant, don't you?

Expansion valve: It is better to use a R-134a valve on a retrofit, but there are vehicles where it is a total nightmare to get to the valve, and some vehicles that do not have 134a valves available (example, older FORD with the block type valve and POA combo, there are others, also). In that case I leave the original valve in place. Cooling will not be optimum, but most times will be acceptible.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

If by chance you have an extra service port on the high side, you might find a switch that could be installed there. That would save opening the system up.

I'm still trying to nail down what statute or regulation requires this, because if it's true it would make all those compressor-death kits (a/k/a $20 "R134a conversion kits" from the parts store) illegal. So far I'm coming up bone dry. Got a cite?



Agreed!



Yeah...kinda like if the red "OIL" light on the dashboard comes on, why, that means you need to add more oil. Fill it right on up to the top, just shy of overflowing.



Agreed...thing is, I haven't been finding much in the way of R134a-specific TXVs. The A-bodies all used this kind of valve:



And nobody's catalogue seems to specify versions for R12 vs. R134a. Have you seen such?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

As far as the valve goes, it can be swapped for the less elegant type with a single bulb that just gets attached to the evaporator outlet and insulated.

I looked real close at the original valve and the pressure is adjusted / calibrated by simply using an allen wrench inserted into the outlet. One would have to set up some sort of test set off car and, I assume, use compressed air or better yet dry nitrogen. The sensor bulbs temperature would need to be controlled during calibration, maybe immersed in water.

In the end the goal would just be to drop the pressure something like 4 or 5 psi., so maybe it would just need to be adjusted that many psi from point A to point B without getting too fancy. Perhaps some trial and error could result in a "rule of thumb" amount to turn the adjustment? Just so long as it does not end up too low and cause frost problems.

My exp valve was not going to fit with everything else that was new anyway, if it had fit I would have used it. I sold it on ebay to a guy with a Cuda who was very happy to get an original and correct valve. Otherwise I would have tried adjusting it just a little and see what happened.