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Old 09-12-2019, 09:39 AM   #1
autoloclys
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Default Ac compressor duty cycle after R134 upgrade

I have just replaced my compressor and resealed the system with the correct o-rings filled with 6oz of pg100 and charged with r134. The system works but the compressor cycles every 10-20 seconds

Is this normal? Itís a bit disconcerting to feel the compressor constantly starting up while driving
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Old 09-12-2019, 11:04 AM   #2
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Yes, that cycling is normal. Find an AC recharge tutorial on youtube that shows the high-side/low-side gauges and you'll see both pressures going up until the compressor kicks in, then the pressures slowly drop, the compressor turns off a while later, the pressures start to rise, the compressor then kicks back on, etc.
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Old 09-12-2019, 02:36 PM   #3
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6 Oz of oil is a lot.

Do you have a pusher fan?
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Old 09-12-2019, 04:22 PM   #4
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I have an factory Efan on the condenser in front of the rad if that’s what you mean

Are the pressures different with r134? Is it cycling more because the system is built on the operating pressures of r12?
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Old 09-12-2019, 06:54 PM   #5
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Temp switch max, fan max.

What is the low pressure side readings. At what pressure does the clutch engage? What pressure does it cycle off. It is normal that the low side would drop when the compressor starts but not so far as to cause the low pressure switch to shut it down which seems to be what is happening.

Could be that you don't have enough gas in it. Or not enough gas is getting through the expansion valve.
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Old 09-12-2019, 07:19 PM   #6
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I was thinking that you were one of the members who swapped in an entire r134a AC system from a '93 (orifice tube, not expansion valve). If so, the low pressure switch, with metric threads, should be #1259519. Try a search on alibaba for INTL-Y098 and see if it still shows up as a replacement.

For the '91-'92 R12 orifice tube systems, the only low pressure switch that was still listed as available was the '91 #1259519, with 7/16-20 threads. This should cross to INTL-Y090 on alibaba.

What system are you running and what parts did you swap for r134a?
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Old 09-12-2019, 07:42 PM   #7
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Depends a lot on ambient temps.

But to me, sounds like you’re undercharged.
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Old 09-12-2019, 07:48 PM   #8
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What was the total WEIGHT of refrigerant you installed?

Did you flush all the old oil? 6 Oz may be close to total capacity.

Did you read the instructions with the new compressor on how to balance it? Or what all did you replace here?
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Old 09-12-2019, 09:50 PM   #9
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Here's a picture of the '93-only factory r134a compressor (click for full size and zoom in):


The label says: "LUB. OIL: SK-20 220cc"

220cc of water is 220 grams or 7.4 oz. Since oil is less dense (it floats on water), say 220cc is ~6.8oz. If you flushed everything, put in a new accumulator, and had nothing in the compressor, then 6.8oz would be needed.

For r134a refrigerant, some post on here said to use 1.62 lbs (25.9oz) for the original '93 setup.
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Old 09-12-2019, 11:03 PM   #10
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It’s a 92 system. Receiver/dryer and compressor are new. All o-rings replaced. Charged with 2.5 cans of r134 which should be plenty. There were no instructions on filling the compressor
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Old 09-12-2019, 11:11 PM   #11
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Quote:
Originally Posted by autoloclys View Post
It’s a 92 system. Receiver/dryer and compressor are new. All o-rings replaced. Charged with 2.5 cans of r134 which should be plenty. There were no instructions on filling the compressor
What does the low side pressure drop to right before the clutch cycles off? Roughly 20psi I’d imagine.

Is the air coming out of the vents cold, as in, sufficiently cold?
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Old 09-13-2019, 11:35 AM   #12
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Assuming youre fast idling while testing pressures?
I usually stick a pencil in the throttle spool to get the revs up.
Without pressure readings and ambient temp its all guesses.
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Old 09-13-2019, 01:13 PM   #13
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OP, thats how my system cycles as well and I have never had a problem. I thought it was an issue when I went to refill R134 earlier this year, but it’s been just fine.
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Old 09-13-2019, 01:23 PM   #14
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Quote:
Originally Posted by autoloclys View Post
Itís a 92 system. Receiver/dryer and compressor are new. All o-rings replaced. Charged with 2.5 cans of r134 which should be plenty. There were no instructions on filling the compressor
Flushed and new orifice tube too? If the orifice tube is partially clogged, cooling will suffer and short cycling may occur.
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Old 09-13-2019, 02:30 PM   #15
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I changed the orifice tube but did not flush the system
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Old 09-13-2019, 08:49 PM   #16
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Quote:
Originally Posted by autoloclys View Post
Itís a 92 system. Receiver/dryer and compressor are new. All o-rings replaced. Charged with 2.5 cans of r134 which should be plenty. There were no instructions on filling the compressor
2.5 cans is not a weight.
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Old 09-13-2019, 10:24 PM   #17
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Quote:
Originally Posted by ZVOLV View Post
2.5 cans is not a weight.
To be fair, Iíve ballparked r134a fills quite a few times on some of my beaters that blow 40F l day in 100F ambient at idle.

That being said, you really should charge by weight as zvolv says. Itís the right way to do it.




Compressor cycles off when low side pressure drop below x psi. Iíve noticed on hot days, compressor will stay on all the time (at idle at least) because itís working very hard to maintain temp. On cooler (75F maybe?) days, when compressor and fan are on, low side pressures drop low enough to cycle compressor off. Just something to keep in mind. If it works well, donít worry about it. Or, evacuate and charge by weight. Even charging by weight doesnít work with r134 conversions because they say "oh about 80-85% of the original r12 fill"
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Old 09-14-2019, 09:36 PM   #18
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Quote:
Originally Posted by ZVOLV View Post
2.5 cans is not a weight.
isnt it? does a 12 oz can of r134 not have 12oz of R134 in it?

i think the official fill is around 28 oz for converting a factory r12 system. I went a little over because of the compressor cycling and i though i hadn't gotten everything out of the first 2 cans. 2.5 cans should be about 30 oz, no?

I had the system filled with R12a (redtek propane mix) before i swapped the compressor and I dont believe it cycled as rapidly as it is currently.
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