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How cold is your A/C?

Discussion in '308/328' started by rocket50, May 28, 2019.

  1. mwr4440

    mwr4440 Three Time F1 World Champ
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    Mine, while in OEM Configuration, worked EXTREMELY WELL ... it REALLY Did.


    UNTIL I .... TOOK IT OUT,

    NEVER to Return.
     
  2. ClydeM

    ClydeM F1 Veteran
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    aint that the truth :)

    I did notice while driving up to Canada - when it rained, the A/C blew cold even when it was 90 outside. When the weather dried up, it pretty much stopped getting cold. I was very tempted to get one of those evaporation misters you see in Vegas to mount in front of the condenser/radiator. I'd be worried about how the water passing through the condenser would affect the components, the duty cycle of one of those small pumps, and how much water (and where) you'd have to carry to stay cool for say an hour drive.
     
  3. EastMemphis

    EastMemphis Karting

    May 25, 2019
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    I assume when it was raining, the sun wasn't streaming into the solar oven (aka windshield) and adding a couple thousands of BTU's to the cockpit...

    If water on your A/C radiator makes it run great, then it's likely you have an issue with airflow through your radiator. It could also be low freon (or whatever) level, or, possibly, a very poorly designed and executed air conditioning system.
     
  4. ZOOOOMZ

    ZOOOOMZ Karting

    Aug 14, 2013
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    FWIW, I just charged the A/C yesterday in my 1988.5 328. For those who haven't read my previous posts, I've redesigned my entire system and converted to 134a, about 6 years ago. Modifications were the Sanden Compressor, barrier hoses throughout (yes, even the ones that run through the rocker panel), Upgraded blower (from RetroAir in Dallas), reinforcing plate, and custom condensation screen in the evaporator, and replacing the copper tube/fin condenser with an aluminum microtube condenser used in the Ferrari 348. I also bent the louvers in the splash shield behind the condenser to nearly full open, to improve air flow. A critical upgrade to the car that made a HUGE improvement in A/C performance is to tint ALL glass (even the windshield) with UV-blocking film from Sunbusters (cost $400 but worth every penny). I live in Austin, Texas, and my car is black, with a Saratoga top. (although I run in the summer with the original fiberglas top, to decrease the cooling load.)
    Now, at yesterday's ambient of 105 degrees F (41C), with a box fan blowing on the condenser (in addition to its own fan pulling air through), engine at 1500RPM and A/C blower knob set to 4 o'clock, I was able to achieve a register air temperature of 44F (6C). I've never before been able to achieve 60 degrees below ambient, but I've been able to reach 37F (3C) register temperatures in the past.
    Even in Texas summers, where the temps are consistently above 100F (38C), the car is cool enough that I can run the A/C at less than maximum to be comfortable.
    One issue is that, after driving for an hour or more, my evaporator coil will sometimes ice, which blocks blower air flow dramatically, so I have to turn down the A/C to thaw the ice, and then I can turn up the A/C again to resume cooling.
     
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  5. Rossocorsa1

    Rossocorsa1 F1 Rookie

    May 14, 2017
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    I have a totally stock ac system on my 89 328 GTB. No tricks, no gimmicks. It blows very cold air. The air isn’t the issue. The reason for the poor AC is that the car has two small, central vents and the windshield soaks up a tremendous amount of UV. It really is that simple.
     
  6. EastMemphis

    EastMemphis Karting

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    #31 EastMemphis, Jun 11, 2019
    Last edited: Jun 11, 2019
    >> my evaporator coil will sometimes ice

    It's very likely that you have too little coolant (134a). A/C is a bit counter intuitive. Too much coolant and the system is too warm. That's because the pressure in the evaporator is too high from an excess of coolant. The compressor can't suck enough of the coolant out of the evaporator to reach the ideal pressure. This prevents efficient evaporation of the coolant inside the evaporator.

    Too little coolant and the evaporator gets too cold in spots and an ice block forms on the evaporator fins. That's because the compressor sucked the pressure too low in the evaporator. Near where the coolant is injected, it gets very cold because it is evaporating too fast, essentially into a vacuum. The rest of the evaporator is too warm though. A perfect balance will yield slightly greater than freezing temperatures across the entire evaporator with the difference between cold and hot spots on the surface being very low.

    Naturally, if the amount of coolant is very low, then the system doesn't work at all.

    The difference between too much and too little in a tiny system like a car A/C can be very small, even a single ounce (~30ml) can make a difference. Having a quality gauge set and knowing exactly what pressures you are targeting can make this an easy task.

    That's my understanding anyway.
     
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  7. thorn

    thorn Formula 3
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    Sounds like a bad expansion valve.
     
  8. Crowndog

    Crowndog F1 Veteran
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    All great advice but I might add that as far as uv tints; they will protect the vinyl and leather from uv damage but will do nothing about temperature. It’s the other end of the light wavelength spectrum that transmits heat. This is the IR (infra red) end of the spectrum. I know of no IR coatings at the present time.


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  9. Crowndog

    Crowndog F1 Veteran
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    Or recovered. I.e. used.


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  10. offtheworkigo

    offtheworkigo Karting
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    Your compressor needs to cycle on and off to stop the evaporator from getting to cold and freezing up. Low on freon could be a problem. The thermostatic switch maybe bad. You may need to turn the thermostatic switch up a little (warmer) to get the compressor to cycle on and off some. The end off the thermostatic which should be connected up by the expansion valve by the little clip on the tubing.
     
  11. mike996

    mike996 F1 Veteran

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    FWIW, you can still find R12 on eBay. The price is, of course, quite high. If you decide to do that, BE SURE, that the listing clearly states it is R12, NOT "R12 compatible!" It would best if it says "DuPont R12" or "DuPont Freon."
     
  12. ferrariowner

    ferrariowner Formula Junior

    Feb 21, 2014
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    Others may have noted this, but If spraying water on your condenser lows the temperature of your AC, then you have a problem with your condenser size or airflow across it.
     
  13. ZOOOOMZ

    ZOOOOMZ Karting

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    Thanks for the comments about possible refrigerant underfill, possible expansion valve malfunction, and the benefits of UV-blocking tint films. I'm no A/C expert, but, with apologies for the very lengthy post, here are some additional thoughts that may help others fighting to optimize their A/C systems' performance:

    Refrigerant fill and system component malfunction - My system's refrigerant fill is optimized for the operating conditions I've chosen, and my expansion valve is working properly. Over the years I've been working with the upgraded system, I've experimented with all levels of refrigerant fill, all the way up to 30 ounces of 134a. To achieve the lowest possible register temperatures, I've determined that the optimal r134a fill for my system is about 10 ounces, which, at yesterday's ambient of 105F gave 44F air temp at the center dash register, at pressures of 28/310 psi measured on a set of quality gauges. According to the P/T curves for r134a, at 28 psi, the corresponding temperature is about 34F, which would not freeze the evaporator coil, so there would be no ice formation. This makes sense, and was proven empirically, since the evaporator did not freeze yesterday under static conditions in my shop, even though it was a very humid day here in Austin.

    I neglected to mention that, in my upgrade, I did also change the expansion valve to one that produces about 8 degrees of superheat. This was also sourced from RetroAir, who developed it for their 308 upgrade kit. I don't know how this compares to the original expansion valve in my 328's system, which was likely optimized for the original system using R12.

    What I believe is happening in my system is this: my test conditions are not identical to the road conditions under which my evaporator freezes. I mentioned that, when I'm charging the system, I use a box fan supplying ambient temperature air to the condenser, which is being pulled through the condenser by its own fan. I'm also charging the system in my shop (not in the sun on the road) with the engine running at 1500 RPM and with the blower fan control set to about 4 o'clock (not maximum). On the road, the system is running under different conditions - the engine is running 3X faster (4-5K RPM) (so the compressor is spinning faster) and the car is moving at maybe 50-80 mph, which supplies a different amount of air to the condenser, cooling it much more than during my charging process. Therefore, I think the real time pressures in the system are somewhat lower on the road than they are at rest with only a box fan supplying air to flow through the condenser. That would explain why, at run time, the evaporator is running at a lower temperature (below freezing point of water) so that ice forms on its fins. FWIW, I think sitting in traffic is like removing the box fan from my static test, dramatically reducing air flow across the condenser. That would explain why my system cools better when moving than when sitting in traffic.

    Elsewhere in this thread, someone suggested that cooling the condenser at run time by misting water on it would also change the cooling system's performance. We can prove this by spraying a garden hose on the static condenser, (which I've done) and does, in fact, result in dramatically lower gauge pressures, which would correspond to lower air temperatures at the register. For my given refrigerant fill, I believe this would lead to icing even under static test conditions, based on my non-water-cooled-condenser static performance of 34F evaporator temperature. In short, misting water across the condenser is another way we could change run time performance by causing lower system pressures and resulting lower air temperatures at the evaporator, and air register.

    I've chosen to optimize my system by charging with 10 ounces of r134a, which, at yesterday's ambient of 105F produced low side pressure of 28 psi (34F evaporator temperature) and register air temp of 44F with the blower fan knob set at about the 4 o'clock position. As suggested earlier in this thread (by EastMemphis and offtheworkigo) that could represent an underfill, since adding more refrigerant is one way we could eliminate the evaporator icing by increasing evaporator pressure. For sure, we could add refrigerant, to increase the run time pressures to prevent evaporator freezing. However, this would naturally result in higher register air temperatures under both static and run time conditions. Of course, there are many other variables at run time, including thermal load produced by the sun beating down on my black car and the human BTUs in the passenger compartment, but I believe the limiting factor on run time cooling is still evaporator air flow. Therefore, I've chosen to optimize my system for the coldest possible air temp at the register, so that the blower-limited air flow across the evaporator will result in the maximum temperature differential (in my static case, 34F to 44F), maximizing the cooling under the blower-limited air turnover conditions in the passenger compartment under actual driving conditions. The penalty I pay for that is the need to monitor the system for evaporator icing, which means I have to turn the system down whenever icing causes a decrease in air flow across the evaporator. Effectively, I've chosen human control over system control, cycling the compressor whenever the evaporator ices.

    My way clearly isn't the only way. For example, one could add more refrigerant, driving higher system operating pressures (and corresponding evaporator temperature), eliminating evaporator icing that way, relying on compressor cycling to control performance. I believe that would result in poorer cooling overall, because we can't drive the car at constant conditions that would hold the evaporator at a point just above the freezing point of water. Ultimately, the choice of refrigerant fill level is a compromise each of us has to make, to optimize system performance according to our own personal preference.

    UV-blocking window-tint films - Crowndog correctly pointed out the difference between controlling energy at the UV end of the light spectrum compared to the IR end of the spectrum. I can only add that, empirically, by testing without and with the UV-blocking window tint film, I've proven that the tint film is responsible for a dramatic improvement in the passenger compartment comfort level with my A/C system's performance. I believe the physics involved may be this: the energy blocking tint film drives measurably lower temperatures inside the passenger compartment, as indicated by the temperature of the dashboard surface, (for instance) or the human's legs, which, in my case, are both now cool to the touch even when the sun is blazing as in Austin's summer. My understanding of the physics is that the dramatic reduction in energy passing through the tint film is reducing the thermal load on the A/C system by lowering temperature in the passenger compartment, which results in improved comfort overall for the passenger and driver. Maybe this is a human perception, rather than a scientifically supported fact, but either way, the overall result is undeniably increased comfort. If you want to maximize comfort in your car, I still recommend that you tint all of your glass, including the windshield, which is legal, but with a less dark tint film than the rest of the car can have.

    As an aside, I would also have had tint film applied to my Saratoga top, because I believe that would provide better results than the original black fiberglas top, but the TCE differential between the tint film and the polycarbonate Saratoga top is too great, which would result in delamination over thermal cycling. So, to maximize comfort, I just switch to the fiberglas top on my car for the hottest season.

    Other factors - I've not previously mentioned this, but another factor that can dramatically affect system performance is the oil level. In my case, after installing the Sanden compressor, the technician inadvertently overfilled the system by doubling the oil charge on an already factory-filled compressor. This led to dramatically poor cooling performance, even though refrigerant charge was sufficient to give normal system operating pressures and temperatures. When the excess oil was removed, cooling system performance skyrocketed. I'm unclear on the physics behind this, but the other trained A/C technician with whom I consulted (not the same one who overfilled the system) speculated that the oil negatively affected heat transfer in both the condenser and evaporator by coating their passages with a thin coat of oil, effectively changing their heat transfer characteristics. As an engineer, this seems plausible to me, but I'm not enough of a specialist to verify it. I do know that this oil overfill is a common mistake that many overlook in troubleshooting poor A/C system performance, which is why I'm mentioning hit here.

    I hope that some of you who are far more subject matter experts than I will weigh in. I'm self-taught in A/C, only because I was sorely disappointed with the service I could get from the best 'experts' I could find here in Austin. I chose to study and learn what I needed to optimize my system's performance, but I'm sure there's a ton still to learn from those who know much more than me.
     
  14. mike996

    mike996 F1 Veteran

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    Good post! Like you, I became an "AC tech" because the real AC experts manage to make the AC worse each time I took it in (twice). The second time they managed to cause the compressor to lock up due to overfilling.

    Re better cooling at low speeds - as I mentioned in a previous post, I removed the OEM louvered grill behind the condenser on my 328. That grill is a major obstruction to airflow through the condenser at low speeds and cooling is noticeably better without it in low speed/bumper to bumper traffic. Not saying it's good, just that it's not as bad! ;)
     
  15. ZOOOOMZ

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    mike996 - I liked your solution to the airflow obstructing grille; I performed my own interpretation by changing the louver angles instead of replacing the louvers with mesh. Your approach probably improved airflow more than mine, but mine has been adequate, with minimal modification to the splash shield, which would probably not get dinged on concours judging.

    Love this Ferrari lifestyle - each can customize to his/her own preference, and we get to share our approaches here for everyone else to appropriate as they wish.

    Think I'll go for a drive in my cool car this afternoon....
     
  16. offtheworkigo

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    I have my new blower motor installed in the case. Before I put in the evaporator in I wanted to check out for any problems. No problem or noises, no leaks. It blows a great great amount of air. I mean a lot. I put the evaporator in with out the front cover on and it blows maybe half the air. You can here the motor is working harder to blower thru the evaporator. IMO we need a new style evaporator for more air flow. A modern design. IMO you will get the air flow you want. Anybody else try the blower motor unit before they put it back in the car? This weekend I hope to have the unit back in and working.
     
  17. offtheworkigo

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    Have the evaporator assembly install. Ready to take it to work tomorrow and evacuate and charge it up with r12. Yes much more air flow.
     
  18. offtheworkigo

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    Here"s a few pictures of my project. Not really difference and others. Thanks to everyone that has posted her on Ferrarichat on how to do this. If anybody is thinking of upgrading there blower motor it's worth it. It blows much more air. I can actually feel the air on my face. Next to check where I have over a 1 volt voltage drop to my fan even with birdmans fuse box. I connect a wire directly from the battery to the fan and I can feel and hear a difference in the sound of the blower motor and feel more air flow. Every little bit will help.

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  19. mike996

    mike996 F1 Veteran

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    With a 1 volt drop it sounds like the factory wiring system is not adequate for the better blower motor. Heck, it may not have been adequate with the OEM blower motor! ;)

    FWIW, a 3% drop is considered maximum allowable for electric motors; 10% for light bulbs. Obviously, the closer to 0 drop, the better.
     
  20. thorn

    thorn Formula 3
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    I'd check for a voltage drop/excessive resistance at the blower switch itself.
     
  21. Jroe550

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    Sep 10, 2015
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    Was driving to my service appointment last week (it was 30 dec c) with AC on high.
    The 328 produces a nice soothing warm breeze. Like a Finish Sauna.
    My son passed out..

    Needless to say it’s not that effective when it gets really hot. (My mechanics checking it out. But it was never amazing)

    Then we picked up / hoped in the new 550 to drive back home and it was like another world of comfort...

    And my son stayed awake too this time..

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  22. Saabguy

    Saabguy Formula 3
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    3M makes one that is almost clear optically. I couldn't find anyone locally that I trusted. Called Crystalline.

     
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  23. Crowndog

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  24. Albert-LP

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    my A/C work great: You can perfectly tune the car's cabin temperature by opening the windows. When it's very hot and the windows cooling is ineffective, I left the car at home... ;)

    ciao
     
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  25. dinonz308

    dinonz308 Formula Junior
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    My A/C is wonderful - blows really cold. Until you get out of the M3 and into the 328, then it's like an oven.
     
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