1972 F-250 R12 system refurb

[JohnHere]

Glad you found and fixed the "re-heat," blend door, and electrical issues.

I could have captured refrigerant analyzed, but thinking just moving forward with 134a conversion mainly for availability of refrigerant for future maintenance.

I think that's a wise move. Even though R-134a appears to be on its way out in favor of R-1234yf, I would expect the former to still be available for quite a number of years due to the large number of vehicles on the road that still use it.

Since the only part left from original system is evap and thermal expansion valve, not sure what capacity it needs. Guess I will start with 80% of 3 lbs = 38 oz 134a and go from there. comp states 175 cc, so 6 oz, PAG46. Have new hoses and new drier. Plan to get new cond. Only have to flush evap/TXV. Assume I should inject solvent in high side.

My references for your truck don't give specific refrigerant and oil capacities, only a note to see the under-hood decal for all three engines available that year. If you're lucky, the decal will still be there. Lacking the decal, figuring on 80-percent of the original charge guesstimated to be 48 ounces with the old York compressor is probably a good start. Fortunately, you already know what the oil spec is for the replacement Sanden compressor.
Converting from R-12 to R-134a has been covered in the Forum Archives, as well as a "sticky" that Tim posted elsewhere. If you search the archives you should be able to find some additional pointers on the charging amount, what the pressures should be, vent temps, etc, rather than repeating all that here.
If you're going to remove the evaporator, I would flush it both backwards and forward (low side to high side, and then high side to low side). If you're leaving it installed, I would flush from the high side to the low side to ensure that you get out all the old oil and solvent.
Use care when cleaning the TXV, don't take it apart, and don't change the setting of the superheat spring. If you change that adjustment, you'll have to send it out for re-calibration or replace it with a new TXV.

[Tim]

That system will be close to 24 ounces of refrigerant. Maybe a little more since the coil will be a little larger. Otherwise, it's just an aftermarket setup.

[rattle_snake]

I drained the oil out of the comp, it is orange and has a sweet smell. Is there any way to easily determine if it is mineral or something else? solvent test?
Mineral is clear and odorless, but obviously any oil in system has been in contact with refrigerant, hoses and so on.

Just wondering if this is a clue to it's mysterious past life.

[Cusser]

I drained the oil out of the comp, it is orange and has a sweet smell. Is there any way to easily determine if it is mineral or something else? solvent test?

When I was working, I could use FTIR spectroscopy to tell in 5 minutes whether the recovered oil was a non-polar R-12 mineral oil or the more hydrophilic R134a PAG-type oil.

If you had small sample of PAG oil to test whether a little water could dissolve in it where mineral type oil would be immiscible, I wonder if that could work as a spot test. I'm 100 miles away from my mineral-type oil and PAG oil right now, so I cannot do such test myself; if that showed a difference, I would try some of the recovered oil.

I could also test any recovered refrigerant by FTIR using a gas cell....

[Tim]

If that is a Sanden.

PAG 100

Sanden import - aka china.

PAG 46.

Easy way to tell. Does it have R12 service ports on the back?

Mineral.

[rattle_snake]

Yes it has R12 service ports on the back. too close together for 134 adapters...

I read the 134 conversion sticky, minimum requirements. I attempted to get a new condenser locally as I already checked fitment earlier as drop in replacement. But that exact model was sold out. So I changed plans again in an attempt to simplify and complete job after dragging on for 5 months.

Drained and refilled comp with Ester/POE 'retro oil' I already had. Got 4.5 oz out, but same amount back in. Comp label calls for 6. No flush of cond/evap. New drier, hoses, orings. Found some 90* 134 quick connect adapter to work with this pump's existing fitting spacing. Put in 3, 12oz cans of 134a (36 total), pressures seem low, 25/250 @ 100 F ambient. Get 20-25* split, 50* out of vents in park, idle. So I stopped there. left heater hoses off at this time to be able to evaluate the A/C by itself.

Went on a 150 mile trip to go off-roading in heat of the day, >100*. Seems to cool cab down from 120+* quick enough after a stop. High fan speed is extremely loud and obnoxious. On the highway I get vent temps in 40s or even high 30s on low fan speed. Didn't want to cycle, so manually shut it down to keep from getting too cold. New water pump/fan belt was slipping, so roadside fix but now out of adjustment range on new setup. Coolant temps stayed below 215, it appears new clutch fan wants to regulate between 200-215. Thermostat is 195. Coolant temps dropped as I climbed steep grades with A/C on. Drove back early this AM, 70* instead of 100" and all temps were about the same, interesting. A/C condenser dumps heat into trans cooler, trans at 140.

So it appears to be a success at this point. Performance seems to be more than sufficient. 134a makes it serviceable. Not the ideal method, but working for now.
Thanks for the help and feedback.

[Tim]

Glad to hear the forum helped on your project.

[tbirdtbird]

Pressures do not seem that bad.
Just spoke to an AC shop owner recently who likes to see 30ish and 260 at IDLE on a 90-100 degree day in the shade. Not a method I have heard of but it sure works for him on systems with unknown charges.
That 260 will come down as car is driven and condenser works better

[JohnHere]

I agree with tbirdtbird. IMHO, those pressures are fine at a 100-degree ambient. Ditto for vent temps in the 40's to high-30's. In fact, it doesn't get any better than that. Do you have a sensor (thermistor) on the evaporator to cycle the compressor to prevent evaporator ice-up? If so, you need not worry. Just enjoy the "cool."

[Tim]

Just a note.

Expansion valve systems will have a completely different set of readings compared to an orifice tube system. So using a general pressure reading format will cause headaches in some cases.

Just a thought.