BII Retrofit, oil and valve question

[KurtC]

I bought my 90BII back in 04 and the ac system didn't work, so I bought some ester oil, o-rings, fancy variable orifice valve, and R134 and did the retrofit. It's been working fairly well, but I think it could do better, so I'm about to pull it all apart again, replace the o-rings, accumulator and flush the system. I don't think I let it vacuum down long enough the first time, and it may be overcharged with oil. Best vent temp I can get is 55 deg. on the freeway. Decent, but not great.

Got a couple of questions about the retrofit:

1. What's the proper amount of oil to add to a flushed system? What viscosity?
2. Is it advisable to use the variable orifice tubes (VOV)? Or does the standard tube work just as well? Standard is the red one, right?

Nearest I can find on the oil level is from an old Haynes book, Heating & Air Conditioning Systems Manual. Evap, 3oz......Condenser, 1oz.....Accum, 1oz....Compressor, 6oz (it says if new, compressor will ship with 10oz, and to pour 4oz out) So, 11oz total oil charge, sound right?

As for the VOV, this article says the orifice size is "Significantly larger than 0.057 at full open and significantly smaller at idle." Red is .062, I think.
http://www.imcool.com/articles/aircondition/VOV1.htm

 

[KurtC]

I did the work last week and am getting a little better performance. I'm not exactly sure how much oil was in the system before, but I did pour a lot out. I blew flush fluid through all the lines, evap and condenser and replaced all o-rings and accumulator. I used 8oz of ester 100 oil and an additional 4oz of some "AC Booster" oil, so 12oz total. Compresser sounds good, so that seems to be a good amount.

I also just re-used my VOV orifice tube, which is working fine. Don't really feel like pulling it apart to compare to a standard red tube, probably not too much difference.

I vacuumed the system down for an hour and added two cans of R134 and another 4oz with two of those booster oil charges. The tag says max charge of R12 is 2 pounds, so 28oz is just a little over 85% of that and it works OK. At the highest blower setting, air temp from the vent is around 50 degrees now on the freeway in 100 degree Texas heat, so it's totally comfortable. 5 degree improvement over what I had before! Doesn't sound like a lot, but it feels a lot better. Also, it'll actually cycle at night on the lower fan settings. Vent temp is around 39 on the 2nd blower setting when it cycles at night. It just can't get cold enough to cycle during the day though, even on a 50 mile hwy trip.

At first, it seemed a little sluggish to bring the vent temp down, and I wasn't 100% sure the R134 charge was optimal. There would be condensation from the evap output, accumulator, and all the way up to the manifold fitting on the compressor, which it would NOT do before. I did a little "tuning" to see if I could get a little better vent temp. I hopped on the freeway for a couple of miles and made note of the vent temp, pulled over, shut off engine and purged from the low side for 2-3 seconds, got back on for a couple miles and repeat. Did this about 4 times, I'm guessing I probably let out 1-2oz (~10 seconds total of purge) but I didn't notice any real difference in vent temp. I did notice a little quicker cool down after that, though, and it's still condensing all the way to the compressor. So, maybe two 12oz cans of R134 would be perfect, or just slightly over that.

My next trick will be to put a dam between the condenser and radiator and add a shroud to the face of the condenser. This should force a lot more air through the condenser on the freeway and will pull more air through it at idle. I'll report back when I get this done.

 

[KurtC]

I found another problem with my heating and a/c system yesterday. The door that closes off my heater core wasn't shutting 100% and letting a little heat through. I don't think the 90BII came with a shutoff valve, so the heater core is always getting hot coolant through it. I clamped off one of the hoses and now my vent temp is crazy cold! Driving along at 45 with blower on high, vent temp will actually get down to 40 degrees. On the freeway, it'll drop down to 38 and will start cycling! It's awesome, never felt this cold in my truck ever. All this was in 100+ degree Texas heat. I don't think there's much need to build the shroud now. I might adjust the pressure switch to cylce a few degrees higher, but I'll run it like this for a week or two and see how it does.

Didn't think a retrofit could perform this well!

 

[RobbieD]

Glad to hear that you had a good experience doing the R134a conversion. Good catch on the blend door.