How cold? can stock AC get.

Discussion in 'The Big Chill' started by flatire, Jul 20, 2009.

  1. 71skylark3504v

    71skylark3504v Goin' Fast In Luxury!

    It already has terrific airflow. What I'm thinking that in the past a compressor blew and set metal chips into the condenser. It did have a rebuilt compressor when I got it. Although it flows free through the condenser tubes it still may have a hot spot that would screw things up. Oh well, what's another $150? Might as well throw one in.
  2. lsrx101

    lsrx101 Well-Known Member

    I don't want to pee on anyones parade, but I really need to call BS on claims of anything less than about 35-38* at the vents. The posted claim of 14* is absolute nonsense unless he is talking Celsius.(57*F).
    The coldest the evaporator itself can possibly get is 31-32*F or it would turn into a block of ice with any amount of humidity in the air at all. A more realistic figure for evap temp is about 34-36* with low airflow. Even at that temp, the air blowing across the evaporator cannot possibly be cooled to that point. It's not in contact with the evap long enough to cool to that temp as it flows through. The air will also pick up latent heat from the ductwork.
    The GM/Frigidaire POA system is probably the best mobile AC system ever installed on a motor vehicle, but it simply cannot overcome the basic laws of thermodynamics. In real life, the very best you will ever see at the vents is High 30's to Low 40's on ANY mobile AC system.
    BuickBuddy's pic shows a very realistic expectation of vent temps, although it can be a 5-6* colder at cruise, assuming that everything in the air distribution system is working as it should.

    Have you ever opened up the evaporator case and cleaned the dirt and debris out? It's really common for the evap to get plugged externally with dirt and restrict airflow. Also, over time the seals on the doors in the air distribution system deteriorate and allow heat from the heater core to flow into the cooled air, thus reheating it. Try clamping off the heater hoses and see if that helps.
    The old single pass condenser is the weak link if you are using R134a, but it can be made to work reasonably well without swapping in a newer style condenser. If you feel a cold/frosted spot on the condenser, that is a restriction. Also check the high side lines and dryer. They should all be hot to the touch right up to the expansion valve. If you feel a cold spot, there is a restriction.
  3. 71skylark3504v

    71skylark3504v Goin' Fast In Luxury!

    I don't believe the doors are the culprit since when I move the lever over, I get a nice thud. However, it seems I have decent airflow out the vents but I guess dirt could be causing it to not be cool.
  4. 12lives

    12lives Gravity is matter warping space-time - Einstein

    If I remember correctly, GM keeps the heater core hot and regulates temperature using the doors and balances the flow with the manual controls or the automatic climate control. In any case, you've got a big heat load sitting just 1/4 inch of plastic away. Add 90+ outside temp and its a challange to get it to work. As isrx101 said, bypass or clamp off the heater core and see if that helps. Then you can tell how much warm air is coming from the heater!


    BUICKRAT Torque Rules!

    Buick, and most gms, have a heater control valve that shuts off the coolant flow to the core when the ac is turned on. If the valve is not working, the ac will not get very cold.
  6. 71skylark3504v

    71skylark3504v Goin' Fast In Luxury!

    I took the blower resistor off and my evaporator is as clean as can be. However, I noticed that my condenser still isn't working for some reason. The temperature of the outgoing refrigerant is just about the same as the incoming line. For some reason, air flowing through it just wasn't cooling it down. :puzzled:I took a garden hose and hosed down the condenser and that seemed to cool the outgoing line, and my vent temps improved.
  7. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    A/C is a must here in Florida so you need all the help you can get. I installed some simple in-line shut-off valves in both the heater hoses in my `65 Skylark so I can shut off the coolant supply to the heater core for the summer, or rather, spring, summer and fall and open them up in the winter if I need them. I got them at Carquest. The part numbers are 277950 and 277951 for the 5/8" and 3/4" hoses.

    Secondly, since R-12 is getting so hard to find and expensive, I switched to Freeze-12. I realize that many say this stuff shouldn't be used but it works just as well as R-12 in my system and it blows about 44-46 in town at the vents, dipping to 37-38 on the road on the open road and I haven't had any problems with it whatsoever. No changes are needed to the system to install it but I did evacuate my system free of the R-12 before installing the Freeze-12.

    Last edited: Jan 12, 2010
  8. lsrx101

    lsrx101 Well-Known Member

    Sweet valves 'Oldie! Many folks are looking for something like that to put in the heater hoses.

    Freeze12 can work very well. It's just R134a with some R142b added to carry the old mineral oil through the system. It will work just as well as R134a, but not better. It worked around the problem of r134a not being able to carry the old lubricant through the system.
    It's not inherently "bad" stuff at all. It had a place when the last R12 systems started springing leaks, when still fairly new, for a quickie "conversion".
    The issue with using it now is that the newest R12 systems are at least 16 years old. The ones we talk about here are 30 or more years old and should really have some PM to be reliable. Most need much more that an evac and recharge.
    Using FR12 now you are still relying on very old seals and a desiccant that is a potential time bomb waiting to go off in your system. It's kind of like putting gas and oil into a car that's been sitting for 20 years and just driving it. It may run just fine for a while but will likely have problems down the road without some initial PM.
    If you were to open the system to replace a component, receiver/dryer or adjust the POA valve for R134a, it would be silly to use FR12 and mineral oil instead of r134a and Ester oil.
  9. Dale

    Dale Sweepspear

    5 yers ago when I bought the '92 Park Ave., the AC didn't work. It seemed to just peter out after I bought it.
    So I took it in to have it looked at.
    Well, after being given an estimate of $2,000 to fix it, I bought a few cans of Freeze 12. What the heck.

    It still blows nice cold air 5 years later! I never have added anymore to it.
  10. lsrx101

    lsrx101 Well-Known Member

    Is that the car in the pic? Niiice.
    Your car probably has a leak around the compressor body seal, really common on those. While they often get worse quickly here in the salt belt, I've seen them leak slowly for many years in a less corrosive environment. When you have to top it off again, just add a couple of ounces of mineral oil to keep the level up.
    As long as it keeps holding, keep on using FR12 in it. It will eventually get worse, but...hey...
  11. No Lift

    No Lift Platinum Level Contributor

    I believe that the vacuum controlled switch in the heater hoses only turns the flow off when the MAX position is activated. At that point you're looking for max cooling. Any other position keeps the hot water running through the heater core so that you can regulate the temp to something above cold. I know when I'm cruising down the highway in my '76 on a warm humid evening it can get too cool in the car. You want to dry out the air and you want some air flow but you don't want it very cold so I turned the heat control slightly to the warmer side with the blower in the middle position and it worked great.
    The valves in the heater lines sounds like the way to go in an area where it stays warm most of the time to positively shut off the heater. Actually it sounds like the way to go for a non-ac car that you want to make a little cooler driving around in the summer. It would keep the heat from even getting into the drivers compartment.
  12. austingta

    austingta Well-Known Member

    On older GM cars, the MAX position closed the fresh air ducts and recirculated the cabin air.
  13. Dale

    Dale Sweepspear

    That's my '96 Riviera.
    My Stepson now drives the Park Ave. :pray:
  14. lsrx101

    lsrx101 Well-Known Member

    I thought that was an awfully pretty Park Ave.:laugh: Now that I know and look close, it's obviously a Riv.:Dou: Duh.

    I have 2 new drivers in the family, I know how you feel. Here, this may help::beer
  15. 71skylark3504v

    71skylark3504v Goin' Fast In Luxury!

    My temperature control lever is supplying vacuum to the water valve all the time, even when it's on cold.:af:
  16. jamyers

    jamyers 2 gallons of fun

    Good info above, here's my $.02 worth:

    * I suggest that you head over to and check out their forums -excellent tech info there. For example, here's a good thread covering a guy with an old Riviera, and how he adjusted his POA and got better a/c performance.

    * A/C system performance depends on a lot of things like ambient air temp, airflow, pressure, etc. IIRC, if you get near or below 45 degrees at the vents you're doing well (that's on 'max', high idle with doors open.) I don't know what my old R12 system blew, but the R134a conversion I did blows 37-44 degrees in 90-degree weather.

    * Don't waste your money on a 'rebuilt' or 'remanufactured' compressor, spend the extra on a good NEW one from a reputable source and be done with it. Too many places do shoddy 'paint-n-ship' work when they 'rebuild', and it's just too expensive (time and money) to evacuate the system, remove a dead compressor, flush the system properly, replace any parts that got plugged with compressor bits, install a compressor, pull a hard vacuum, check for leaks, install a new receiver/drier, pull another hard vacuum, recharge with refrigerant, then check to see if everything actually works. It's cheaper in the long run to spend the money up front - been there done that.

    * Old GM a/c systems like ours (POA / Expansion valves, A6 compressor) are awful hard to beat, and from a design standpoint are arguable FAR superior to modern Cycling-Clutch, Orifice-Tube (CCOT) systems. R12 is a far superior refrigerant (over everything else out there), that's why it was chosen back then when a/c system performance was the driving factor behind a/c system design (instead of modern concerns like mileage and environment).

    If I had a decent source of affordable R12, I'd have replaced/upgraded the old hoses (just because) and stuck with it. But I didn't, so I converted to R134a and am happy with the results.

    As far as converting to R134a:
    * Remove all the hoses and flush, flush, and flush the system. Lacquer thinner works well. Then flush everything again. You must get ALL of the old oil and any trash out of there.
    * Replace the hoses - R134a has smaller molecules and will leak out of R12 hoses, especially old ones
    * R134a 'wants' a bigger or more efficient condenser (different thermal characteristics) than R12, although our old tube-n-fin condensers are often large enough to work well. If you want a better condenser, get a TRUE "parallel-flow" condenser, they're about 30% more efficient. But keep in mind that if you EVER have a compressor failure, the condenser often becomes the filter and plugs up, requiring replacement. GM makes a filter that goes between the two for just such an event. sells both PF condensers and the filter.
    * POA valve will want to be re-adjusted for R134a - this is something you can do pretty easily yourself if you have an air compressor. I forget exactly how, but there's a how-to at Basically, you adjust a nut inside the end of the POA valve to get a target pressure reading.

    Don't mean to sound like a commercial for, but every time I research mobile a/c parts and stuff they come up as the best source of info and quality parts at good prices.
  17. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    About 2 1/2 years ago I had the system open to upgrade the rest of the car (engine, trans, rearend, suspension, disc brakes, quicker steering, pretty much eveything mechanical was upgraded). It has factory a/c with an A6. Everything worked fine up to that point but when I put it back together the compressor was noisy so I replaced it with a remanufactured unit. I hope the reman unit has modern seals in it. As long as I had it apart I also replaced the POA, expansion valve, and dryer and put new seals in most everything, except at the condenser. I replaced the oil with fresh esther oil and evac'd it for about 30 minutes or so. So far so good. No complaints with the Freeze 12.

  18. lsrx101

    lsrx101 Well-Known Member

    Oh! You pretty much rebuilt the system? Good Job! You can't beat a fully functional POA system with an A6 compressor for performance. Enjoy!

    The Freeze 12 will work just fine as it's basically R134a. It was just unnecessary because you changed the oil to one compatible with R134a. There's no longer any mineral oil for the R142b to carry, so it's just along for the ride. No issue there.

    Your new A6 will have all modern HBNR rubber in the case seals and the old style ceramic shaft seal. The ceramic shaft seal will work fine with R134a but you may eventually get the age old oil slinging issue from around the clutch. GM always claimed some oil slinging was "normal", but they never specified how much was too much. A new double lipped rubber seal can be retrofitted to the A6 to prevent it but there's no need unless the ceramic seal fails. I don't know of any manufacturer that installs the lip seal in their units. Keep it in mind for future reference.
  19. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    Thanks, I'll do that. So far I've seen no oil on the compressor, but then again nothing lasts forever.......does it? :pray:

  20. No Lift

    No Lift Platinum Level Contributor

    The compressor on my '76 Century seems to be slinging oil out of the clutch area and it seems to be excessive. Can that double seal be fitted to the compressor while the unit is still charged? I have a clutch removal tool and service manual so I'm half-way there.
    If it can't I just have to install one of those shields that GM had on some of the cars. Now I know that it was there just to keep the oil from flying all over the place.

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