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Thread: Trying to fill A/C system; blows hot air and high side has low pressure

  1. #61
    Administrator Ron's Avatar
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    Quote Originally Posted by jangell View Post
    I was wondering about the 3 oz thing. A quick video I found today showed refilling a Sanded-style condenser with 6 oz of PAG, like you said. I did change the evaporator and condenser (and everything else), so based on what you've said that 3 oz is probably not enough. I have a can of full PAG that I haven't used yet.
    I'd add 3 oz. If you need more later, you can put it in with a charge can.

    Quote Originally Posted by jangell View Post
    I am constantly getting which side is which turned around in my head. I need to print that diagram and stick it to the wall or something.
    Maybe this will help. The flow: compressor "D"=High Side -> condenser -> orifice -> evaporator -> accumulator -> compressor "S"=Low Side

    Quote Originally Posted by jangell View Post
    Here's a bad picture of the back of the compressor, showing the "S" and "D" connections. The disconnected line is the one that I originally thought was the high side line, then figured was the low side based on the readings from the gauges. Turns out it's the high side line, but not the high side of the compressor.

    Attachment 60709
    No, that is the high side of the compressor that is hooked up in the pic. What hose you have hooked to it I can not tell. That is the high side gauge hose hooked to it, of course, assuming the other end is correctly hooked to the gauge manifold.....

    Quote Originally Posted by jangell View Post
    I just went out and put a loose zip tie on one of the lines and slid it down from the compressor to the frame to make sure I absolutely know which hose is which. The line from the S side of the compressor is definitely going down the driver's side of the frame towards the condenser.
    That is wrong. "S" comes from the Accumulator.

    Quote Originally Posted by jangell View Post
    Now the question is how to swap them. I'm hoping I can just switch the hoses at the compressor (assuming the connections are the same size), but I think one of them has a threaded connector while the other doesn't (it's held on by a bracket, like in the original setup), and that concerns me a bit. I'm not going to be able to go back out and take things off today (way too hot and humid), but it'll be cooler tomorrow so I'll check it then. It would be so very convenient if I could just switch them.

    Looking at the parts manual diagram https://store.delorean.com/c-303-7-2...ve-system.aspx I have the routing physically correct, except for the fact that these are not the S and D ports on my condenser, which makes it incorrect.

    This is the thread where I asked for recommendations for the compressor, BTW: http://dmctalk.org/showthread.php?16...ecommendations. I'll note that Farrar's picture of an Eagle compressor installed shows the low side on the passenger side, just like on my compressor, but I have the hoses connected wrong. And the oil drain plug is in the same place, so it seems I have it mounted correctly.
    You said before that Farrar's was "similar", iirc. A lot of those colored caps can fit either side, and the back plates can be different on the same model as mentioned....I think you should forget everything and stick to the chart.

    Put whichever hose that goes down to the condenser on the port labeled "D", the high side, and go from there. (Same for Red gauge hose, assuming it is correct on the gauge's manifold...) I like your pull tie trick! Use it to confirm the rest, especially in the nest up front (no matter what ;-).

    Quote Originally Posted by jangell View Post
    I wasn't sure if I could feel the suction by disconnecting the line turning it and seeing if it sucked or blew while the clutch was engaged. That was the theory, anyway. Assuming the ports are labeled correctly on the back of the case, I don't need to do this test.


    YW!

  2. #62
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    Quote Originally Posted by Ron View Post
    I'd add 3 oz. If you need more later, you can put it in with a charge can.
    Sounds good

    Maybe this will help. The flow: compressor "D"=High Side -> condenser -> orifice -> evaporator -> accumulator -> compressor "S"=Low Side
    Thanks -- I'll copy that down for reference. I'm also starting to think "D" for "driver's side", but I know that's very specific to our cars and not a general rule, so I shouldn't get used to it.

    No, that is the high side of the compressor that is hooked up in the pic. What hose you have hooked to it I can not tell. That is the high side gauge hose hooked to it, of course, assuming the other end is correctly hooked to the gauge manifold.....
    Yup -- the high side gauge hose is hooked to hose in the discharge port, but that hose goes to the accumulator, not the condenser, which is wrong. And once it's moved to the suction port, the blue (low) gauge hose should be connected to it.

    That is wrong. "S" comes from the Accumulator.
    Right -- sorry, I meant that's how it's connected at the moment, and is indeed wrong.

    You said before that Farrar's was "similar", iirc. A lot of those colored caps can fit either side, and the back plates can be different on the same model as mentioned....I think you should forget everything and stick to the chart.
    Good point. I'll stick to the chart.

    Put whichever hose that goes down to the condenser on the port labeled "D", the high side, and go from there. (Same for Red gauge hose, assuming it is correct on the gauge's manifold...) I like your pull tie trick! Use it to confirm the rest, especially in the nest up front (no matter what ;-).
    Thanks for your patience and help with this -- I'm almost there... pretty sure, anyway.

    -- Joe

  3. #63
    Administrator Ron's Avatar
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    By Jove, I think you've got it!

    Don't cheat using the pull ties.

  4. #64
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    I should just stick blue and red pull ties (or electrical tape) at intervals down the appropriate lines so I never mix them up again.

    -- Joe

  5. #65
    Senior Member Bitsyncmaster's Avatar
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    If your hoses can't be swapped, maybe if you pull the back plate and rotate it 180 deg. (if possible) it may reverse the hose connections.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #66
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    Some more tips to confuse you;
    Make VERY sure the pressure hose (discharge hose) is SECURELY attached to the frame where it passes by the steering shaft. The bolt can rip the hose apart if it touches.
    Make sure the hoses do not put stress on the evap or condenser fittings. They are aluminum and will fracture. No twists or pulling.
    The oil drain for the compressor is supposed to be on the bottom.
    You can "regenerate" an accumulator with heat and vacuum but if it is contaminated with old, acidic oil (or the wrong type oil) you cannot clean it. Best to replace it after you have done your pressure testing and before your final evacuation and charging.
    D is for Discharge. It is the port that the high pressure hot gas comes out of to go to the condenser coil to turn into a warm liquid. S is for Suction and is the port the warm low pressure gas enters the compressor to be turned into a high pressure, hot gas.
    The discharge hose runs along the left, driver's side,to the condenser.
    If your manifold gauge set is not working correctly get it fixed or get another. It is dangerous to use equipment on high pressures that is faulty. The valves MUST seal properly to the yellow hose (center port). Always verify the gauges read 0 before connecting. Adjust them if necessary. Any good gauge set has gauges that can be zeroed. Blue to the suction (low pressure) side and red to the discharge (high pressure) side. Yellow to your charging can and/or vacuum pump.
    On most A/C systems the high pressure port is AFTER the condenser coil. On Deloreans they put it right on the discharge of the compressor. You must remember that because your reading will be very high because the gas has not been cooled so evaluate your readings accordingly by the temperature/pressure chart for the refrigerant you are using.
    You should pull a vacuum of at least 50 microns and hold it for 30 minutes to remove all air and moisture. 30 is even better.
    David Teitelbaum

  7. #67
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    Success!

    I easily swapped the hoses at the compressor (they're not threaded or anything like that, and I don't know why I thought they might be; they just press into place with O-rings and that center bolt/plate arrangement), replaced the accumulator and orifice tube (the latter was actually stuck in the end of the hose and the plastic case had a break, so that didn't help), vacuumed it for over an hour, and filled it with R-134a.

    I took it for a test drive to pick up a vent thermometer after I lost the one I bought a few weeks ago for this purpose. On the way home, I read about 50 F for the center-ish vent (my vents are in the knee pads), but the external temp sensor on my car is reading 100 F, so I think that's pretty good. I'll have to see what it's like on an 80 degree day.

    There is more to do, though:
    - I added ~3 oz of PAG 100 to the compressor, which itself came pre-filled with 3 oz of PAG 100. It seems to be working fine.
    - I haven't adjusted the low pressure switch for R134a yet.
    - I need to rig up some kind of A/C high idle though MegaSquirt. I stalled a couple of times when stopping, and even had some trouble restarting the car with the A/C engaged, so I need to look at my idle settings. I have issues with low RPMs when coming to a stop anyway, so this isn't unique to the A/C -- it just made it worse.
    - I aimed a box fan on high at the radiator while filling.

    One thing I'm trying to figure out, though, is that I only put in about two 12 oz cans. The pressures seemed ok, with the high at about 275 on this 90-100 degree day, and the A/C seems to be blowing cold enough. However, I just re-read Dave's post about how the location of the high side port on the DMC means that the reading should be higher than what most charts show. I was filling with the engine at 900-1000 RPM. While the compressor cycled just fine up until the end of that second can (at which point it just stayed on), some reading afterwards suggested that I should have tried a higher RPM so that the compressor would compress more, and the pressures would go higher.

    To be honest, though, at the moment I'm just happy that it's working at all, but I'm guessing that I don't have enough refrigerant in it and I need to fix that.

    Thanks!

    -- Joe

  8. #68
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    Did you get the car up to 50-55 MPH? Doing this for say 5 to 10 miles will give the orifice tube a good chance to seat in. You might feel the difference when it does. I know I did.

    My $0.02

    David B.

  9. #69
    Administrator Ron's Avatar
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    Quote Originally Posted by jangell View Post
    One thing I'm trying to figure out, though, is that I only put in about two 12 oz cans. The pressures seemed ok, with the high at about 275 on this 90-100 degree day, and the A/C seems to be blowing cold enough. However, I just re-read Dave's post about how the location of the high side port on the DMC means that the reading should be higher than what most charts show. I was filling with the engine at 900-1000 RPM. While the compressor cycled just fine up until the end of that second can (at which point it just stayed on), some reading afterwards suggested that I should have tried a higher RPM so that the compressor would compress more, and the pressures would go higher.

    To be honest, though, at the moment I'm just happy that it's working at all, but I'm guessing that I don't have enough refrigerant in it and I need to fix that.

    Thanks!

    -- Joe
    Congrats!!!
    Now finish up :
    You have 24oz 134a in it now. You need 31.6oz total, as David said in post #2, so it needs 7.6oz (~215 grams).
    Assuming you don't have the scales and tap can that normally goes with the gauges, you can still install the correct amount:
    Get an inexpensive scale (<$15 at Walmart, etc.) that can measure in 1/10oz (or grams).
    Weigh and record (Varies by brand!):
    12oz can of 134a (Ex: 32oz)
    Recharge hose (Ex: 34oz)
    Add together (Ex: 32 + 34 = 66oz)

    The new can is holding (12oz - 7.6oz) = 4.4oz (125 grams) too much refrigerant...
    Attach the can to the recharge hose and place on scales.
    Bleed off until it weighs 4.4oz less. (Ex: 66 - 4.4 = 61.6oz (1746 grams)).
    [Practice placing the assembly where it will stay w/o touching it while it bleeds off first!]
    Shut the recharge hose's valve immediately.
    The correct (remaining) charge is in the can.

    Connect HIGH side of gauges with all valves shut!
    Start the engine, let idle -- Turn the air on max cool & max fan.
    Keep one eye on the high side gauge at all times for safety (see gauge manual)!
    Keeping the can upright, connect the recharge hose to the LOW side.
    Be patient until the can is totally empty.
    (If you keep shaking the can you should notice it get cold then go back to ~normal when it is empty.*)
    Disconnect the recharge hose assembly.
    The total charge should be correct.

    Pressure Check:
    Connect the LOW side of the gauges.
    Adjust idle to ~1500 RPM.
    Wait until engine is fully warm, if needed.
    Compare the readings with the following WS Manual (R12) chart below.
    Make sure that you take both readings when the compressor turns OFF!!!
    Your pressures will be higher since you are using 134a!

    Since you are using 134a, you need to calculate the correct(ed) target pressure for the high side:
    Add 40F to Ambient temp then look the value up in a conversion chart (Conversion Chart, Details HERE).
    (Ex: For 90F ambient. 90 + 40 = 130F, which corresponds with 198.9psi in the chart. So expect ~189 to 235psi+)
    Don't push your luck in 100F+ climates -- Adjust the pressure switch so there is no chance of it getting over 300psi.

    DMC-ACPressureData.jpg

    Wear safety goggles. Don't pollute. And, above all, don't tell the cook if you borrowed their scales!

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