Hello to All,
My question is regarding a 1981 3/4 extended 4x4 w/351 windsor. I recently put a Eddelbrock performer package on motor cam,manifold,carb. I am pleased with the results. In the process I removed all the smog sh-- and old R12 ac compressor and want to convert to 134. If anyone has done this i could sure use some input on what parts I need to change out and what can be reused and also where the parts are found ( doner vehicles) and how compatable 302 parts are with the windsor, also what were the last production years for the windsor and the 302
Thanks Aaron
Put all your old A/C system back on, evacuate the system, and then throw in some 134a with the oil already in it.
Some people say change this, add that, which may make it work better, but it will work by just putting the gas in after you put a vacuum on it. I have done it before. If you happen to find out you have a leak or something is broke like the compressor, it's not that big a deal since the gas is not that expensive.
Franklin2 is correct in that it will probably work at least for awhile, Problems: 1. If the system has been open for a few days the desiccant in the accumulator/dryer is likely saturated with moisture and moisture + refrigerant = acid (not good). The desiccant in most R12 systems don't work with R134A anyhow. At least change the accumulator dryer to one that is rated for R134A. 2. While doing that get a new orifice tube red/white versus original blue/white. You probably can't get the old one out of the old accumulator without destroying it anyhow. 3. You need to get as much of the old mineral oil out of the system as possible. Mineral oil isn't transportable by R134A so it's just taking up space that could hold more refrigerant. 4. Get ester oil (poly olester) for your system, it is compatible with mineral oil remaining in the system. PAG oil, which is used in new vehicles, is not nearly as good for conversions especially if you don't completely flush out the old oil. Google "R12 conversion" or "R134A conversion" for more info.
+1 on the red tube and new accumulator, cheap insurance. Flush the old oil out using a/c flush. You can use shop air at @ 20 psi to clear out the flush if you dont a have a friend with a flush gun. Also you can adjust the Low Pressure switch to accomodate for the difference in pressures between 134 and 12, about 1/8th to 1/4 turn on the screw between the pins ought to do it. I have mine tweaked to run at 33-34 degrees at the center vent. I find my self turning it down a lot. An o-ring kit for your truck should be about 6-7 dollars, I would replace all the o-rings while you have it apart. You can get an air operated vacum pump from Harbor freight for around 10 bucks, works just fine If you have a good enough air compressor. The evaporator/condensor/compressor on your truck will work just fine with r134a
Archion, what size compressor do you use for the vacuum pump? Several years ago I tried one of the air operated pumps using my C-H 2-1/2 HP piston type compressor w/12 gal. tank. The compressor ran continuously and I could get only about 10" HG vacuum, which isn't good enough to get all the moisture out of a system.
you can do all the above or you can just drain the r-12 out add pag oil and a good qualty r-134 freon like freeze on or something of a good qualty trust me that the qualty of freon matters more than changeing all the other stuff i have done the swap on more than a few cars/trucks over the years and they all still work fine 2-3 yrs later
I don't like using the PAG oil either. I have heard it doesn't mix well with the original oil. Since I don't flush the system, I use the 134a that has the ester oil already in the can. Like someone else said, the old r12 oil just lays in the system and doesn't hurt anything with the ester oil.
We use those air/venturi vacuum pumps on industrial machines where I work. They are air hogs, and require a lot of flow. They will pull down into the high 20's though.
29.6" Hg. = ~10,000 Microns results in a water boiling point of 53 Deg. F. which is low enough to get most moisture out of a vehicle system. The proper desiccant can get the remaining. For the average home user I doubt the venturi pump can achieve anywhere close to that. A good refrigeration vacuum pump can get to 25-50 Microns. On the environmental test chambers that I used to be responsible for, we always went to 500 Microns or less.
Piffery, the vacum pump requires @90 psi at min of 4.2 cfm. My 28g gallon Cambell Hausfield Lowes special supplies 6.1 cfm at 90psi. It is the 6.25hp 28 gallon 150psi model, probably around 4 years old now, I bought off of my neighbor for 100 bucks, barley had any hours on it, not even dusty. It pulled the f-150 down to 29 in about 10 minutes, I let it run for 25 and sealed it, let it sit for about an hour, came back still had 29, all was good.
As far as pag with the mineral oil, it turns into something similar to brake fluid, eats the rubber parts out from the inside. Ester is best for a retro-fit on Fords.
The orifice tube and the switch adjustment are the biggest changes. It is STRONGLY recomended to change the accumulator, not just for the trash that is in your old one, but also the original dessicant is NOT compatible with r-134a.
Also you can adjust the Low Pressure switch to accomodate for the difference in pressures between 134 and 12, about 1/8th to 1/4 turn on the screw between the pins ought to do it.
Quote:
Originally Posted by Archion
The orifice tube and the switch adjustment are the biggest changes.
I got an "extreme climate variable orifice valve" at Advance Auto for about $32 that is supposed to turn the truck into a meat-cooler.
Where is this LOW PRESSURE SWITCH, and which way do you turn the screw ?? Between what pins ??
Does this change pressure readings on the gauges ??
Of all the hundreds of A/C threads I have read, this is the first mention of adjusting a low-pressure switch that I have read.
Also, with R134a, on a ninety-degree day, what readings should the high and low sides show with a properly charged system ??
When you change the orifices, and monkey with the pressure settings on the switch, you are getting into territory where you need to know what you are doing.
Slapping the 134a into the system gets it cool enough for me, and everything is set as original. I have to admit though I have never changed the gas over without changing the accumulator, since each time I swapped a system over, it was because the compressor seal was leaking, and they would not warrenty the new compressor without buying a new accumulator.
If you want to get the system working top notch, then you can change all this other stuff around, but like I said, you really need to know the ins and outs of A/C systems.
The low pressure cycling switch is on the side of the accumulator. Unplug the harness connector and you can see the adjustment screw between the switch terminals. Turn CCW about 1/8-1/4 turn to lower the temperature of air out of the center vent to about 34 or 35 Deg. F. after all the other mods have been done. I don't charge with R134A by pressure. I put in R134A at 85% by weight of the original R12 charge. I.e., If the original R12 charge was 48 oz. then use .85 X 48 = 40.8 oz. of R134A. I always install a High Pressure Cutout Switch to prevent damage from over pressure. See: Classic Tool Design AIR CONDITIONER HIGH-PRESSURE CUT-OUT SWITCH KIT : JC Whitney: Auto Parts & Accessories
This switch screws over my old existing R12 high-side gauge-port and the wire from the low-pressure switch then gets also routed through this switch, right ??
Do I simply screw this switch on with my system still charged; or, do I have to evacuate the system, remove the valve-core, and then install ??
Yes, Counter-clockwise. Max of 1/4 turn. But only after everything else is done and only if you need a little more cooling. Be aware that you may not be able to achieve 34-35 Deg. F.
Yes, High-side port and wired in series with the low-side cycling switch wire going to the clutch.
I always install the HPCO switch while the system is open in conjunction with the other work. I remove the old R12 Schraeder valve before installing but I'm not absolutely sure it's necessary, there may be a valve pin depressor on the end of the HPCO switch fitting.
