So...I swapped out the POA eliminator for the original POA set at 26.5. Charged the system and sorry to say results were no better....actually worse.
95 deg ambient temp: pressures are 285 high, 32 low , vent temp 60 deg at 2000 rpm. I performed the on car POA test to see what the low side would be with blower disconnected. Pressure dropped to 27 (where it should be). I then sprayed the condenser with water and the low dropped to about 27-28 and the high to around 210. When I kept the condenser wet the vent temps dropped to around 50 deg. There was sweat on the inlet side of POA and the outlet was frozen (this only occurred after spraying water). There is roughly 2.5 lbs 134 in the system (I don't weigh it because of system modifications (condenser, sanden compressor, etc) so I don't know how much it actually requires. The engine fan is the stock fan for the truck and the clutch is new. Condenser is mounted in the same place as the original and spacing to radiator is close to original. I am all out of ideas maybe an electric fan would fan would help, but I don't think that's the problem, This system was designed to work without one and should be fine without one. It would take a really skinny fan to fit between the condenser and hood latch mount. Anybody got any ideas? I'm running out of patience and sanity here.
70 GMC, 134 retrofit problem
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Re: 70 GMC, 134 retrofit problem
A couple of things to consider
Your Sanden replacement is 8 CID/ rev. At idle it will never do what the 12 CID A6 would.
The parallel flow condenser is a good thing, but it has to have good airflow. You mention spacing, but the more important issue is coupling. A weather strip at the edge of the condenser to keep the air from bypassing the condenser on the way through the radiator can help. Every bit of air the factory fan & shroud moves should go over the condenser. You do have a fan shroud right?
Charge level
In a custom system it is always an unknown, but with a TXV you can make some observations while charging - using the sight glass. An overcharged PF condenser does not perform well. The water spray at idle showed a significant change. Could be a little overcharged, or just poor airflow.
Your Sanden replacement is 8 CID/ rev. At idle it will never do what the 12 CID A6 would.
The parallel flow condenser is a good thing, but it has to have good airflow. You mention spacing, but the more important issue is coupling. A weather strip at the edge of the condenser to keep the air from bypassing the condenser on the way through the radiator can help. Every bit of air the factory fan & shroud moves should go over the condenser. You do have a fan shroud right?
Charge level
In a custom system it is always an unknown, but with a TXV you can make some observations while charging - using the sight glass. An overcharged PF condenser does not perform well. The water spray at idle showed a significant change. Could be a little overcharged, or just poor airflow.
Re: 70 GMC, 134 retrofit problem
Thanks for the input bohica2x0. I decided to take it out for a drive a see what it would do. Got vent temps down to around 46F driving at around 65 mph. This is not terrible considering with the 700r4 I am only turning around 1600 rpm at 65. I need to change my rear end gearing but that will have to wait a while. Drove around town a little and the temps didn't drop off too bad. It cooled the cab OK, but i was hoping for a little better, but considering its a high of 105 today I'll take what I can get. I will remove the tape from the sight glass and take a look. Its close when driving, but just sitting in the garage a t 2000 rpm with no air flow the the vent temps wont go much below 55-60 deg. everything else looks good, the outlet of the evap was sweating pretty profusely and the back half of the POA was frosty. I'll watch it and see how it does.
1 question ---when looking at the sight glass what exactly am i looking for? I understand that this was an important part in determining proper charge with R12 and wanting the sight glass to be free of bubbles, but with 134 it is my understanding that it is not possible to be bubble free. Am i wrong?
1 question ---when looking at the sight glass what exactly am i looking for? I understand that this was an important part in determining proper charge with R12 and wanting the sight glass to be free of bubbles, but with 134 it is my understanding that it is not possible to be bubble free. Am i wrong?
Re: 70 GMC, 134 retrofit problem
Don't worry about the sight glass with R134a.
Re: 70 GMC, 134 retrofit problem
While you might not be able to completely clear a sight glass on some conversions, a gushing stream of foam still tells a story.
The advice to ignore a diagnostic tool comes from years old garbage conversions - leaving all of the mineral oil in place, undercharging the 134a to hold the pressures to a safe level, adding ester oil etc. Yes, the sight glass looked like a swirling toilet bowl full of diarrhea. The conversion worked the way it looked too.
Commercial refrigeration systems use sight glasses on refrigerants other than R12. There is no reason that a miscible refrigerant oil in subcooled liquid refrigerant would not present a homogeneous appearance - perhaps a bit cloudy but still an indication.
The advice to ignore a diagnostic tool comes from years old garbage conversions - leaving all of the mineral oil in place, undercharging the 134a to hold the pressures to a safe level, adding ester oil etc. Yes, the sight glass looked like a swirling toilet bowl full of diarrhea. The conversion worked the way it looked too.
Commercial refrigeration systems use sight glasses on refrigerants other than R12. There is no reason that a miscible refrigerant oil in subcooled liquid refrigerant would not present a homogeneous appearance - perhaps a bit cloudy but still an indication.
Re: 70 GMC, 134 retrofit problem
Always good to learn something new.bohica2xo wrote:While you might not be able to completely clear a sight glass on some conversions, a gushing stream of foam still tells a story.
The advice to ignore a diagnostic tool comes from years old garbage conversions - leaving all of the mineral oil in place, undercharging the 134a to hold the pressures to a safe level, adding ester oil etc. Yes, the sight glass looked like a swirling toilet bowl full of diarrhea. The conversion worked the way it looked too.
Commercial refrigeration systems use sight glasses on refrigerants other than R12. There is no reason that a miscible refrigerant oil in subcooled liquid refrigerant would not present a homogeneous appearance - perhaps a bit cloudy but still an indication.