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I can't find the a/c master thread

H

h(iroll)er

Member
Joined
Sep 28, 2009
Location
Austin, tx
its that time of year should be plenty of a/c posts I see none

that mast post is great but it only recommends components. doesn't give diagnosis.

I have a 1992 na 240. put tcp 4 seasons compressor, crossflow condenser, new drier and variable oriface tube last year. paid some really low tier chain to evacuate and charge up. I had 60-65 degrees at vents.

wanted it colder this summer so I added a spal fan behind radiator and vintage air trinary switch at drier. I figured if I was gonna get things really cool I needed a true high pressure cut off. compressor seemed to short cycle too much since the day it was charged. I put oil with dye in and uv showed no leaks, so I added more freon. using gauges it was 25 L side and 150 H. compressor could not engage for more than 2 seconds. after about 10oz more of r134a pressures were 45 and 225 at 95 degrees outside today. It went from 62 at vent to 46 degrees!

all sounds well but the weird thing is I let it idle for close to 30 min and the compressor never kicked off. if I reved it up to 3000 the compressor would kick out and in rapidly. never fully take a break.

is this -normal? low on freon? overcharged? bad wiring?
 
here's the vintage air trinary switch wiring. I know its not causing the compressor to be constant on because when I was low freon it would only run for 2 seconds at a time. mostly stayed off.
IMG_3817 Large.jpeg
 
Try removing your added black wire - from your drawing, it's shorting the "A/C On" signal to ground when the "trinary switch" closes.
 
the one in with the fan relay? I added that awhile back because according to Dave barton that high pressure switch only affects the fan coming on. that switch wouldn't never ground out so I added a ground wire since no one sells that switch anymore.

I disconnected my ground like u said tho. now that I have good pressure in the system fan runs fine so maybe now the switch worked.

I drove it around today and ye compressor won't stop and I find im getting 10-20 degrees high at the vents when Im driving around. vent air is humid until I come to a stop.

I let freon out until I was down to 30 and 200psi. compressor wouldn't cut off still. I added another can thinking maybe there's just not enough freon to hit the high pressure cutoff... nope one more can and my pressures are back around 45 and 250. compressor still runs non stop
 
Ok update:

I am now running the $17 amazon lp switch. Nice cuase its adjustable but still waiting on the right thing from fcp euro. I have it set were it clicks off around 23 psi like the dave barton bible says it does factory. Now my compressor clicks off as soon as i hit 1500 rpm but i still worry cuase at idle it runs non stop.

Ac fan runs with compressor pretty much. Maybe i need a lil more freon to get the hp side up past 250? That would cause the fan to go off but what causes lp side to drop pressure at idle in a good system?
 
Helpful but wild it doesnt even say what the ambieny temp is for their readings.

After putting on the “factory” low temp switch im at 35 and 200. Lost alot of freon with that cheap plastic switch.

I think for 90 degrees ambient temp im low on both sides so i can fill
 
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