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Thread: Ac issues

  1. #1

    Default Ac issues

    This one is a little strange. My buddy does ac and has taught me a thing or two but itís I think a combination of issues maybe. When I turn the car on and let it idle with the ac going itíll get down into the 40s with ambient temps in the 80s. It can do this indefinitely it seems but the compressor stays on. If I drive it while in motion itís around 40* and stays there until I stop. While in motion I can feel the compressor cycle. Now after I drive it and park it the compressor stays running like before but the ac blows around 60* and will get warmer if I turn up the fan speed. Why does driving it make a difference? It can be idling at full operating temp and still be in the 40s and when I get back itís still at full operating temp. Could it be a faulty pressure switch or overcharged? With said ambient temps the low side is around 30 psi which is on the low side. Any info would be great.


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  2. #2
    Beater gonna beat sly's Avatar
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    If it's a little low on refrigerant, the increased pumping of higher RPMs will allow the compressor to draw down the low side below the cut-off pressure. This can cause the evaporator to freeze up (get too cold and create ice on the surface). This is much more common with R12 systems. R134a systems won't cool that low and don't do this that easily.

    Another possibility is if the liquid line has drooped and is close to the exhaust manifold as this will help warm up the liquid before it gets past the expansion valve. This usually induces damage to the liquid line and it doesn't last long in this condition, so I doubt that's the issue.

    The last think I can think of is the blend door on an automatic system... if the temperature control valve hose is not attached to the barb on the air plenum at the firewall (behind the glove box) it won't pull air over the coil that controls the valve and it may soak the cooler air from behind the dash and not cool as well.

    Of course, if the blend door itself has no seal left or the door is broken and not holding full closed for cool, it'll do this as the heater core warms up as it's mixing hot air in as well.

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  3. #3

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    I know itís not low as Iíve put in more than enough at this point. Originally I put in what would be the equivalent to the original spec converted to r134a. 70% comes to mind but I forget. Anyway since then Iíve added some with the same result and it seems to not make a difference and I hate to keep adding refrigerant.

    All the lines are new and in stock locations. Also it has manual controls.

    Could it be overfilled and the condensor gets heat soaked?


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  4. #4
    I'm an air-conditioned gypsy gadget73's Avatar
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    too much refrigerant makes for high pressure, and that increases temperature. Clue there is the compressor will not cycle, low charge will have it cycle.

    Charge is somewhere in the 70-80% of the R12 amount but you can also judge it by evaporator outlet temperature. When the evap is fully flooded, the outlet pipe temperature will start to drop considerably. Since I don't have an AC machine and have no way to figure out whats in the system to do a top-up by weight thats how I do it. Basically when the drier gets cold with the engine at ~1800 rpm, its pretty close to right. High and low side pressure will help confirm its not over or under-charged. I usually aim for low side pressure in the 20-25 range, basically as low as you can get it without the compressor kicking out. The lower the pressure, the colder the refrigerant but unless the evaporator is full of cold refrigerant the vent temperature won't be very cold.



    The other thing that makes the AC start to suck as the engine heats up is a bad fan clutch. Heat from the radiator cooks into the condenser and that makes it less effective. Poor airflow makes this much worse.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

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  5. #5

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    The fan clutch is new but I guess I shouldnít rule it out. Do you think itís overcharged? Maybe having the compressor run continuously while driving for 20-30 mins at a time is causing it to heat soak. I have everything to wire in a pusher fan but Iím afraid if I do Iíll need to do a 3g swap which will just add more complexity to things lol.


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  6. #6

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    Did you replace the AC cycle switch with one set for r134a? I've had some cars (like my CV) where it made a big difference, and some where it didn't make much difference at all. My CV was one of the ones that made a difference. The Low and high pressures are a few psi different; on the CV it made the difference from cycling all the time at idle to just cycling every few minutes (although the temps were pretty close inside the car).

  7. #7

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    To be honest I donít remember. I believe I originally had a 134a switch but it fit poorly and leaked so I got an r12 switch. There are no markings on it but I believe thatís whatís on there now.


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  8. #8
    I'm an air-conditioned gypsy gadget73's Avatar
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    unplug the pressure switch and back the screw out about 1/4 turn. You have now converted your R12 switch to R134a. Cutout with 134a should be right around 20 psi, its like 28 with R12.

    hard to tell if its overcharged without high and low side gauge pressures.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  9. #9

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    Iíll try that out tomorrow. I have an old set of gauges that the high side is broken and the new ones I have are ebay specials. I doubt theyíre accurate. Iíll see if I can get a reading tomorrow though.


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  10. #10

    Default

    I adjusted the screw as advised and tried putting the gauges on. The high side wouldnít go on so I took it off and was greeted by a nice leaking shrader valve... luckily I have the tool with the ball valve built in to swap valves with the system under pressure so I did just that. It lost a little refrigerant during the process but itís probably not a bad thing. So I started it up and still no cycling. But I put the fan speed up to max and it was about 50* then I took it for a spin and it dropped a little then sat outside idling and it was steady around 48-50*.

    One thing I forgot to mention before was that in my first post I noticed all the issues with the fan speed on low. When turning it up the temps climbed. So it only cools right when the fan is on low.


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  11. #11

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    I have a laser thermometer and when playing with it a little when the fan speed is turned up the higher the temps are and the lower the fan speed the lower the temp is. My guess is the evaporator isnít getting as cold as it should.


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  12. #12

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    Did you replace the orifice tube when you switched from r12 to r134a? Did you flush out the evaporator with the orifice tube out?
    Gadget, I didn't know that the switches were adjustable. Handy info!

  13. #13

    Default

    Yes on both. When I bought the car it had nothing so everything is new except for the condensor but like I said it was cleaned. I need to get a new set of gauges and get an actual reading for you guys.


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  14. #14

    Default

    So I took a quick pic of the pressures at idle after it warmed up.



    Ambient temps are in the low 90s with high humidity. Low side seems low and the high side is a little high. And the high side was fluttering 20 or so psi the whole time. My guess is air in the system.

    Also the compressor would cycle like normal a few times when first started then stay on.


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  15. #15
    I'm an air-conditioned gypsy gadget73's Avatar
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    looks like 30 on the low and 215 on the high? Honestly looks pretty good for 90F. What does it do with some throttle? I usually wedge a dime or a penny under the throttle stop screw. That puts the rpm around where cruise speed is. Expect the low to go lower and the high to go higher.

    Flutter on the high side could be internal valve problems with the compressor. Its a 6 cylinder pump, and if one of those reeds is bad it will dance pretty rapidly. Unless its just the hood vibrating and making the needle dance.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  16. #16

    Default

    Iíll check tomorrow. The hood does vibrate but I donít think thatís what caused the bouncing. As it was idling it was only getting into maybe the low 60s high 50s. Also thatís a new compressor, supposedly.

    Anyway Iíll test it, take it for a spin then test again tomorrow.


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  17. #17
    Beater gonna beat sly's Avatar
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    Rule of thumb is that the high side on a 134a system that uses an orifice tube should be about 3x what the ambient temp is in Fahrenheit. So about 250-270 ballpark. The system may be a little low, but it's not far enough off to really give the issues you've been dealing with in my opinion.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  18. #18
    I'm an air-conditioned gypsy gadget73's Avatar
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    yeah I wouldn't say its overcharged either. If the charge is low enough that the compressor cycles off, that would do it.

    Another thought, if the blend door is not fully to cold, you'll get poor AC performance. It will also show as low pressure since its not getting a full heat load. Bad foam on the door causing a poor seal, or if someone replaced the evaporator and did not put the foam back around it won't work so well. A dirty evaporator will also cause poor performance. If you pull the blower out, you can see part of it. Might be worth doing to see if its all covered in crap. No filters on these so whatever comes in through the blower goes into the heater and evaporator cores.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  19. #19

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    Evaporator is brand new so I doubt thatís the issue. I checked for air leaks around the evaporator, none. Blend door, all the way closed. No leaks that I can find. So I did what was suggested, I added some more refrigerant and I revved it for at least 10 seconds or so and the low side dropped to about 20 psi but the compressor didnít cut out. It still did drop though so what does that point to? Not enough airflow across the condensor?

    Also when I added refrigerant when I opened the valve it would climb 5 psi then fall back down and took forever to charge.

    Today is probably a little cooler than the last time I checked but with the fan motor on high it dropped to about 56* or so, so I guess more refrigerant is needed.


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  20. #20
    I'm an air-conditioned gypsy gadget73's Avatar
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    The pressure differential will get higher with more RPM because the compressor is doing more work. Not too surprising really. If its a problem with airflow on the condenser usually the pressures just go up. I usually run it steady at ~1800 and mess with it from there.

    Could be the charge connections are a bit crappy. The original ones with my gauge set had some internal problem where they had very restricted flow. It barely charged and it just didn't respond like it should. I've also had issues with the can taps not always giving a full puncture or depressing the valve. Newer cans use a different tap too, not sure what combo of stuff you're using. I don't exactly know what will happen if you use the older style tap with the new self-sealing cans.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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