85 RX-7 r-134a conversion

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YellowFB
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85 RX-7 r-134a conversion

Post by YellowFB »

I've been working to convert my 85 RX-7 with factory air from r-12 to r-134. I first checked it's integrity and found it held vacuum nicely for 30 minutes.

I put in about half a bottle of Ester100 oil through the high side hose while pulling a vacuum with the low side and spun the compressor by hand and it immediately spun smoother, then let it pull a vacuum for another 30 minutes.

Going off the label on the Nippendenso compressor, it originally held around 2+lbs of r12, I understand you'd put in about 75-80% of that with r-134.

I put one 12oz can in and the compressor came to life and it started cooling inside the car but not great. My confusion is that with only 1 can, the low side pressure was already at 55 psi at about 85* F, which is what most charts list as the proper charge. When I started putting the second can in, one of the lines coming off the condenser failed.

I will replace the line and install a new drier, but I'd like to prevent this from happening again. The compressor label shows a much higher minimum low side pressure than what I've seen on most r/12 or r/134 pressure charts, at least at usual temps. Does that high of a low side pressure seem right or should I stop adding refrigerant at 55 psi, marginal cooling would be better than none.

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Tim
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Re: 85 RX-7 r-134a conversion

Post by Tim »

It sounds like you're using one of those low-side-only charge bottles. You cannot get an accurate performance of an ac using those types of items, IMO. A complete set of ac gauges is required for proper ac work. Those pressures listed on your compressor on not system operating pressures. 55PSi with an expansion valve system is pretty high. I suspect and pressure-related issue with this type of conversion. Without a high-side reading, it's tossing darts a wall trying to figure it out.

Capacities
Refrigerant Type R-12
System Capacity 1.5-1.7 lb (US)
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tbirdtbird
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Re: 85 RX-7 r-134a conversion

Post by tbirdtbird »

Agree with Tim.
Those pressures are NOT operating pressures, they are test pressures, ie max pressures the system will take. Rather useless info, IMO.

Your operating pressures will be closer to the numbers you are accustomed to seeing....ie Low 30 ish Hi 200 ish

What did you do about the mineral oil that was already in the system?
And how much is half a bottle of oil? Can you better quantify that?

So, you blew a hose or a hard line? In that case better to replace them all
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YellowFB
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Re: 85 RX-7 r-134a conversion

Post by YellowFB »

I figured out it wasn't the lines, it was the end cap of the condenser that failed, it's blowing out of a predrilled hole in the condenser bracket. I'd heard the original didn't do well with r-134 anyway at least. Good to know the label is not showing the usual operating pressures, thank you.

I unhooked the compressor and drained the mineral oil while spinning it by hand, it was a 8 oz bottle of Ester100, I went off a Nippendenso chart for the 10P compressor and added about 4-5 oz, I'll add more to compensate for new parts and some that blew out.
tbirdtbird
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Re: 85 RX-7 r-134a conversion

Post by tbirdtbird »

If you only drained the comp then you are oil logged. There was still more mineral oil in the hoses, cond, evap, and FD.
You need to start over.
You also need a pro manifold gauge set that reads both hi and lo pressures, and those pressures should be noted at 1500 RPM, max cool, max fan, recirc, doors open, minimum of 80F ambient (and report the ambient) and report the center vent temp.

If your low was 55 then your hi was probably about 400, because you have too much oil in there.
Be advised that the condenser fin spacing for 134 is tighter than for R12, so an R12 cond will not work very well, and that will make your vent temp higher than you want and your high pressure higher than you want. You want the largest parallel flow condenser that will fit.

Tim, the site owner, also sells AC parts and tools, and has good prices, and good quality. It is always worth checking his prices before buying stuff. And whenever I order anything it arrives in 2 days.
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