How to get AC colder

[coupecustom]

I started a WTB thread earlier today because I was looking to swap out my under drive pulley for a factory crank pulley in hopes of making my AC compressor run at its normal operating RPM at idle...thus cooling the Ty a little more. Well I basically did a test with a vent thermometer and ran the truck at 2200 RPM for 5 minutes. Temp dropped about 4 degrees. My thought here is that it would be about the same as if I had a factory crank pulley.

The vent thermometer showed that at idle, with the AC on full blast, I was getting about 68-69 degrees. Running the RPM to 2200 about 64-65. Still not enough to be comfortable, but I'm still thinking of trading my under drive pull kit since it is indeed better.

Point is, how can I get the ac system colder? I've read that with R134a in these trucks I should run a different low pressure switch...well that's really only if the compressor is cycling....mine isn't. I don't have any covering on the accumulator...not sure if that would help much. Just looking for ideas since its hot as hell here in FL. Thanks

 

[Slyclone]

Re: How to get AC colder

Could just be low on the charge.

Try a $10-$15 can of charge. Or whatever one comes with the reusable hose...

 

[randy merritt]

Re: How to get AC colder

Some good info here:

http://www.syty.net/forums/showthread.php?t=13323&highlight=parallel

In chat, DaveP wrote up several things to do to increase the performance of the R134 setup. They included a different orifice, adjusting the low pressure switch (which has a screw on it), and going to a parallel flow condenser (not necessarily needed). I saved a copy of his advice via a screen shot in Notepad, but I have lost it. I did everything Dave suggested, and my a/c works great.

 

[SY2932]

Re: How to get AC colder

Prolly gonna cost a bit more than that if he is still running R12 in his truck...

AC can be a very complicated endeavor. If a low charge is keeping the compressor for cycling, you can "trick" it by unplugging the pressure switch and putting a jumper in the plug. If adding refrigerant doesn't make it get cooler and the compressor is cycling, you could have a plugged orifice tube. If that be the case, you will have to open up the system, replace it and the accumulator/drier, pull it down with vacuum pump for at least an hour to remove the moisture and then recharge. Personally, I would NEVER just add refrigerant without monitoring both the low side and high side of the system. To do that or any troubleshooting of an AC system, you need a manifold gauge. Bottom line is if you don't have tools and knowledge to mess with it, you are better off paying someone else to service it :2cents:.

 

[coupecustom]

Re: How to get AC colder

I should probably give some background here on my specific AC system.

When I got my Ty it had no compressor so, last summer, instead of just adding a compressor I decided to take on the whole system and properly update it to 134a.

I put in all new parts: New Compressor, new parallel flow condenser (same one as you Randy), new Accumulator, new low pressure switch, new orifice tube, new evaporator, and new to me but used SYTY factory AC lines.

I then went ahead and had the system professionally oiled and charged. I have gauges and a vacuum and have done it myself in the past, but I did not want to mess with a leak test that the pro's would do for me. There is still die in the system and I have looked around for leaks and there are none that I could find with my naked eye. I would really need the glasses to tell if there was a leak somewhere.

When I had the AC system charged, I was told that the new orifice tube I had was not working...it was one of those fancy ones that's supposed to drop the temp further than normal. They ended up putting a factory replacement orifice tube in instead.

As for the low pressure switch an adjustable one would be nice. Mines the factory 93 one without adjustment. The only reason I see not replacing mine at this point is that the compressor is continually running. My understanding of the adjustable low pressure switch is that it gives you the ability to change where the charged air would reach a low pressure setting and therefore change at what pressure the compressor would cycle off. Since the temperature when low enough is also low pressure, this is the cause of what we refer to as cycling....a compressor shutting off when the pressure is low enough.

So with mine continuously running at idle and not cycling that means the pressure is never getting low enough to cause the compressor to turn off. There could be insufficient refrigerant in the system, thus indicating a leak since it was fine at one point. I'll need to put my gauges on and see what the high and low pressures are and I guess start from there.

My question is what should my high and low side pressures be for a 134a system that would indicate that it is fully charged?

 

[DaveP]

Re: How to get AC colder

Here's a couple of easy to check ideas:

With the system running, is the accumulator cold? In FL humidity, the can should be very wet and cold to the touch. If so, the refrigerant system is operating correctly. If the can is dry and warm, it isn't.

If the can is dry and warm, feel the tube at the very bottom of the evaporator case, where it goes into the case, after the orifice tube. If it is cool-ish here, but the outlet going into the accumulator is warmer or warm, this usually indicates a low charge, or plugged orifice tube. (I'm a little perplexed by the fact it isn't cycling, as cycling almost always accompanies poor cooling caused by low refrigerant).

If the accumulator is cold and wet (refrigerant system performing adequately), check the temp door cable adjustment to be sure the temp door is fully closed. Remove the access panel in the rear of the glove box. Put the temp lever to full COLD, and then check that the lever on the heater box is fully closed. If not, slide the wire in the clamp as needed. You'll figure it out. Easy-peasy, and not fussy.

System pressures for a properly charged system vary somewhat depending on ambient temperature, heat load in the cabin, and airflow through the condenser. I don't have access to my shop literature, but off the top of my head, but R134 low side should be <30psi with low blower speed, and high side shouldn't be over about 200-225psi with adequate condenser airflow.

You're going to HAVE to retrofit the adjustable pressure switch and connector to your 93. The R12 setting is about 28-30psi. For R134 you need 20-22psi. The difference is about 12°F in evaporator temp. You'll have to do this to get adequate cooling once you get this other stuff sorted out.

There's some ideas.

 

[berzerker]

Re: How to get AC colder

could be a lot causing the low vent air temps . All the above mentioned , could be as simple as the blend door not fully closing , low refrigerant charge , plugged / blocked orfice tube , junk compressor . Does the compressor cycle on / off normally ?? Need to know cycle interval times .. should cycle on for 45 seconds then off for 10-20 seconds . With a/c running is the low side hose going into the evaporator getting cold to the touch - low side hose is the fatter of the two . btw the air coming from the vents should be around 45 min to 55 max temp wise for a good working system .

 

[berzerker]

Re: How to get AC colder

could be a lot causing the low vent air temps . All the above mentioned , could be as simple as the blend door not fully closing , low refrigerant charge , plugged / blocked orfice tube , junk compressor . Does the compressor cycle on / off normally ?? Need to know cycle interval times .. should cycle on for 45 seconds then off for 10-20 seconds . With a/c running is the low side hose going into the evaporator getting cold to the touch - low side hose is the fatter of the two . btw the air coming from the vents should be around 45 min to 55 max temp wise for a good working system .[/QUOT

Treed -
never mind Dave covered all the bases

 

[drturbo69]

Re: How to get AC colder

Coolant temps. & radiator condition? Clutch fan pulling air across condensor? Have seen new compressors installed with too much oil? Front mount intercooler? And all the above.

 

[coupecustom]

Re: How to get AC colder

AC is frustrating to me :rant:

So, I went ahead and checked out the blend door. Its definitely closed on the coldest setting. I'm unable to move the cable any further.

Now on to the accumulator. Its definitely wet, it drips all over the place and is nice and cold to the touch. My one concern about the accumulator though is that it sits so close the waste gate exhaust for the down pipe. So, what happens is the top of the can is cold and wet, while the bottom is less cold and not wet, since the moisture evaporates quickly at the bottom, being so close to that much heat.

Lets talk gauges. I'm in the deep south of Florida (Lehigh Acres). Temp outside while working with gauges was 91 with 53% humidity. When I had the fan on high the high side pressure reading was about 225 psi. The low side was about 35-40psi fan on high. Fan on low it would bottom out at about 25psi.

Temp in the cabin got to a best of about 62F on fan high and 55F fan on Low. This is with the vent temp in the center vent.

Through the process of getting these numbers I had put a little refrigerant in and realized I had to much so I took some out. The data above is the result of the best that I could get in the end. Its an improvement...but I think I should be able to get better.

As for flow over the condenser. I run an RPM dual electric fan setup and I can feel the air pull with my hand in front of the condenser, so my opinion is that it's pretty good. I know humidity is a huge factor with its efficiency though.

Last, Dave, I want to ask about how this adjustable pressure switch could help me? I'm guessing it can't yet, since I'm unable to get the low pressure to sink below 22psi. My best number was 25psi, and even with my 93 low pressure switch the compressor did not turn off. That leads be to believe that my pressure switch is probably faulty anyway since it should probably cut the compressor off when its below about 28psi.

What should my next steps be? I've thought about removing as much refrigerant as possible to see if I could at least get the low side psi to drop to around 20 psi. Theoretically that should actually be colder too, but I believe there comes a point when you can't get the low side pressure any lower and the temps actually start to rise since there's not enough refrigerant in the system.

 

[randy merritt]

Re: How to get AC colder

I put an insulation sleeve off of a mid 90's full size truck on my accumulator. It took a little modification, but it went on.

 

[SY2932]

Re: How to get AC colder

I have gauges and a vacuum and have done it myself in the past, but I did not want to mess with a leak test that the pro's would do for me. There is still die in the system and I have looked around for leaks and there are none that I could find with my naked eye. I would really need the glasses to tell if there was a leak somewhere.

With that being said, you are light years ahead of most on this problem. I always get a chuckle when I go into the parts store and they have those "get your AC cold again with this can" deals. If it was really only that easy :lol:...

My question is what should my high and low side pressures be for a 134a system that would indicate that it is fully charged?

Of course there are variables that come into play but this is a chart that I use for R134a:

outside temp * low side * high side * center vent temp
60 F ** 28-38 psi * 130-190 psi * 44-46 F
70 F ** 30-40 psi * 190-220 psi * 44-48 F
80 F ** 30-40 psi * 190-220 psi * 43-48 F
90 F ** 35-40 psi * 190-225 psi * 44-50 F
100 F * 40-50 psi * 200-250 psi * 52-60 F
110 F * 50-60 psi * 250-300 psi * 68-74 F
120 F * 55-65 psi * 320-350 psi * 70-75 F

A quick rule of thumb for the high side is you double the ambient temperature and add 50 to get in the ballpark where it should be pressure wise. Funny thing is, I don't even have AC in any of my cars. But my wife and some of my clients need theirs... Sounds like you are working towards a solution, please keep us posted on your efforts !

 

[jimmyz79]

Re: How to get AC colder

I put an insulation sleeve off of a mid 90's full size truck on my accumulator. It took a little modification, but it went on.

X2 - I do this on all my vehicles...

 

[DaveP]

Re: How to get AC colder

Looking at the pressures Mike put up your center outlet temp should be in the 40's°F. The refrigeration system seems to be functioning adequately.

Here's what I'd check first. Then keep reading. Remove the blower resistors from the case, and cover the opening with duct tape.. These are on the downstream side of the evaporator. Fire the system up, and put your thermometer through the duct tape and compare the reading to your center vent temp.

I'd recheck the temp door. Push the red plastic retainer out of the mounting boss, so the outer jacket is loose. With the dash lever in full-cold, push on the jacket so that the door is full-closed. Now check the plastic retainer index to the boss. Just because the dash lever is full-cold, doesn't mean the door itself is.

Another possibility is that the foam seals on the temp door are so deteriorated that it's allowing too much heat to bypass the fully closed door. Check the A/C temp on a first start in the morning. If the center vent temp is low, but comes up as the engine warms up, I'd suspect the door seals. And easy work-around for this would be to bypass the heater core for the summer.

You are 100% correct that the 28-30psi R12 pressure switch is not affecting or "hurting" performance at this point. The purpose of the cycling is to hold minimum] evaporator temperature just above 32°F to prevent evaporator icing. (A bad thing). As long as the heat-load exceeds the system's capacity to get the evap temp down to 32°, no cycling is necessary. Where the cycling usually begins is at highway speeds where condenser airflow, and compressor speed improve the system's efficiency to the point that icing is likely to occur.

You have a wet and cool accumulator, and the pressure are just about right for the test conditions. If the check in the resistor opening is cooler than the center temp, heat is being introduced from somewhere. Recheck the temp door.

 

[coupecustom]

Another possibility is that the foam seals on the temp door are so deteriorated that it's allowing too much heat to bypass the fully closed door. Check the A/C temp on a first start in the morning. If the center vent temp is low, but comes up as the engine warms up, I'd suspect the door seals. And easy work-around for this would be to bypass the heater core for the summer.

I only had time for this test this morning. And you are correct, as the temp of the engine came up, so did the temp on my vent thermometer. All in all about 6 degrees before I turned the truck off.

So, I'm going to make a guess here, that in order to redo the foam on the door the dash and entire box would need to come out? I believe I saw the door when I replaced the heater core last summer.

I still have to go through the red clip adjustment before I do anything drastic with the door. I'll get to it next weekend...spending this week in Orlando with family celebrating my sons first birthday


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[Quickstop [UK]]

Re: How to get AC colder

This is a great thread. Hope you get it fixed.

 

[randy merritt]

Re: How to get AC colder

I only had time for this test this morning. And you are correct, as the temp of the engine came up, so did the temp on my vent thermometer. All in all about 6 degrees before I turned the truck off.

So, I'm going to make a guess here, that in order to redo the foam on the door the dash and entire box would need to come out? I believe I saw the door when I replaced the heater core last summer.

I still have to go through the red clip adjustment before I do anything drastic with the door. I'll get to it next weekend...spending this week in Orlando with family celebrating my sons first birthday


Sent from my iPhone using Tapatalk

I just loop my heater hoses whenever it gets warm enough to need the A/C. That takes the mixing door out of the equation.

Given how far south you are, you may never need to use the heat at all.