Hi guys, I have a '01 and I have a question about the a/c, I do a/c work on CAT equpiment but the computers in here are kinda throwing me off, I'm not sure to what extent they control this system. What's happening is that after about an hour or shortly after drive, the a/c begins to fade out, fan still on high sounds like its blowing but nothing comes out. But if you sit a while it will go back to normal. I thought that there may be some moisture in the system freezing the evaporator so I got a new dryer, vacuumed it down and replaced it and refilled. a/c blows colder now(46 awsome degrees in sunny south florida! ) but the problem still presists. I was curious if anyone else has experianced this and if they have what the solution was. Or if the post I was looking for ever had a result to it. I did a search about a week ago and found some info on my problem and I read something about a high pressure switch I tried to find this thread and it kept giving me the message that no search results were found but i know its out there soo here I am. If there somthing that somone might suggest I have all the equipment to vacuume it down again if I need to. Thanks in advance guys I know you all have the knowledge!

 

Hi, what you describe could be a freeze up situation, which is usually caused by short refrigerant, when it happens , if you turn the temp to max heat,(90), that should open the temp door to the heater and you should get full air blowing out again, if that happens , you are freezing the evaporator, and need to adjust your refrigerant level, or it may be the control valve in the compressor. SEE BELOW.
Good Luck
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The basic operation of the variable displacement orifice tube (VDOT) refrigeration system is the same as for conventional A/C systems. The VDOT refrigeration system utilizes a variable displacement compressor which contains seven cylinders; a V7 compressor that can maintain the automotive air conditioning demand under all conditions without cycling the compressor.The basic compressor mechanism is a variable angle wobble-plate with axially oriented cylinders. The control of the compressor displacement is a bellows actuated control valve located in the rear head of the compressor which senses suction pressure. The wobble-plate angle and compressor displacement are controlled by the crankcase-suction pressure differential. When the A/C capacity demand is high, the suction pressure will be above the control point; the control valve will maintain a bleed from the crankcase to suction; no crankcase-suction pressure differential; and the compressor will have maximum displacement. When the A/C capacity demand is lower and the suction pressure reaches the control point, the control valve will bleed discharge gas into the crankcase and close off a passage from the crankcase to the suction plenum. The angle of the wobble-plate is controlled by a force balance on the seven pistons. A slight elevation of the crankcase-suction pressure differential creates a total force on the pistons resulting in a movement about the wobble-plate pivot pin that reduces the plate angle.

The compressor has a unique lubrication system. The crankcase-suction bleed is routed through the rotating wobble-plate for lubrication of the wobble-plate bearing. The rotation acts as an oil separator, which removes some of the oil from the crankcase-suction bleed, rerouting it to the crankcase where it can lubricate the compressor mechanism.

The compressor, depending upon engine usage, is cut-off under certain conditions, such as wide-open throttle, low idle speed, low ambient air temperature, high power steering loads and high engine oil or engine coolant temperatures. The V7 compressor has a mechanical destroker that will destroke during engine speeds of 3000-3800 RPM.

When the air conditioning system is turned OFF, the refrigerant in the system will flow from the high pressure side of the evaporator tube orifice to the low pressure side until the pressure is equalized. When the engine is turned to OFF without first turning OFF the A/C system, this may be detected as a sound of liquid flowing (a hissing sound) for 30-60 seconds and is a normal condition.
EDIT--You want to keep the ref pressures on the low side up enough to maintain NO LESS than 34 degrees at the plates, if you are getting 46 at the vent, my suspicion is the you are getting 30 or less at the plates

 

Well, that is some really good info. I actually know exactly how it works. Some of the stuff i work on has this type of pump for the hydraulic functions but anyway. I highly doubt that there is a compressor failure. and I know the freon is charged well I did the work myself. If this thing has no need for cycling then why are the pressure switches in the system?

 

HI, There is only one pressure switch, it is a combined pressure switch for high and low pressure, it is there to protect the system in the event of higher or lower than proper pressures.-See Below
The ref charge should be 1.75lbs , on the early models it was specified at 1.50lbs, but was changed due to freeze up complaints. There was a chart posted on a thread a while back giving very good charging instruction, if you don't have a scale it is best to charge at 2000 rpms to get the proper charge. It is possible to have a faulty switch that is allowing the comp to operate at a pressure less than 30psi, and allowing freeze up conditions. But in theory due to the nature of the system,(non cycling system), that should not happen unless the ref charge is not quite proper as can happen over time.SEE BELOW for replacement instructions
Good Luck
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A/C Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The PCM converts the voltage signal to a pressure value.

The A/C system can be engaged by pressing the A/C switch. The A/C switch will illuminate when the A/C switch is pressed to the on position. Pressing the A/C switch the control module grounds A/C request signal circuit from the powertrain control module (PCM). The following conditions must be obtained before A/C compressor engagement is allowed:

The engine coolant temperature (ECT) is less than 121°C (250°F)
The engine RPM is more than 550 RPM
The A/C pressure is between 207 kPa (30 psi) and 2826 kPa (410 psi)
The A/C request signal circuit is grounded.
Once engaged, the compressor clutch will be disengaged for the following conditions:

The throttle position is 100 percent
The A/C pressure is more than 2826 kPa (410 psi)
The A/C pressure is less than 207 kPa (30 psi)
The engine coolant temperature (ECT) is more than 121°C (250°F)
The engine speed is more than 5,500 RPM
The transmission shift
The PCM detects excessive torque load
The PCM detects insufficient idle quality
The PCM detects a hard launch condition
When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

Automatic Operation

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Pressure Sensor Replacement
Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
Tools Required
J 39400-A Halogen Leak Detector

Removal Procedure




Disconnect the refrigerant pressure sensor electrical connector.



Remove the pressure sensor (1) from the evaporator tube - front.
Remove and discard the O-ring seal from the sensor port on the evaporator tube - front.
Installation Procedure




Install a new O-ring. Refer to O-Ring Replacement .

Notice
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.


Install the pressure sensor (1) to the evaporator tube - front. Tighten
Tighten the sensor to 4.75 N·m (42 lb in).





Connect the pressure sensor electrical connector.
Leak test the fittings of the component using J 39400-A . --------------------------------------------------------------------------------

 

GetCrazyKid..... just to add a few thoughts. Many years ago I had a 1968 AMX (poor man's Corvette) which, BTW, was number production number 000149!! But I digress.... anyway, it had mosisture IN the system. What i remember is that before it would stop cooling, it would blow frosty (visible) air for a minute, then warm air. Turn it off, let the ice at the expansion valve orifice melt, and then it would be fine for a while.
BUT if I read your post correctly, you are saying that when it happens, there is no air blowing from the vents (did you check the floor and defroster vents?) -- is that correct? It would be unusual in an auto AC to get a complete freeze-up of the evaporator coil because of the high volume of air that typically moves over the coils, but hey, it's muggy in FL. Which brings me to this..... if you experience longer times before "failure" when using higher fan speeds, OR if on re-circ (i.e. not letting in all our Florida humidity) than you do at low fan speeds or on "fresh air," such would definitly indicate a likelihood of ice blocking the evaporator.
What are your low and high side pressures at 2,000 rmp? ...and at what ambient? I ASSume you know to keep fan on highest setting, AC at lowest (65?) setting, and cirulation on "fresh air" ... i.e., max demand.
for temp/press chart see
http://forums.corvetteforum.com/show...ghlight=ac+101
Lastly, and before this becomes a book, IF the system passes all charge/pressure tests, you might consider removing some of the oil (there is a plug on the compressor crankcase -- but DE-PRESSURIZE the system first!) If it weren't illegal to vent R134a, you could just hold down one of the Schraeder valves to let refrigerant escape rapidly, which would carry a lot of oil out with it... esp if the system had been run only for a few minutes so oil hadn't had time to settle in the crankcase. i don't know if I made this up, but I have a feeling that too much oil can screw things up in a myriad of ways. Full oil charge is, as I recall, 9 oz BUT don't quote me on that. Oh, and that's a fully solvent flushed system and dry (no oil) compressor. And for all of you reading this post that are facing the prospect of compressor replacement, rocco has an awesome step by step linked from this corvetteforum. Direct link is http://trans5.com/docs/C5%20AC%20Com...eplacement.pdf
Keep it cool!

 

Vacuum leak? Did you look under the battery for signs of corrosion?
Debri in the blower housing?

 

Man guys thanks for the info this is some really good stuff i can use to check more thoroghly. to answer as many q's as possible. yes i did check for corrosion where the battery goes when i changed the dryer, there was none and thank god its got a red top optima battery . as far as the settings when the vehicle is running I did as you said. It works good one short trips but im gonan have to make time for a long one to see where the air is flowing when the failure happens. I did not think to check if it was going to the defrost or the foot vents, as well as the drain tube! its around the mid to high 90's the past few days here and i have my gauges home this weekend so i'm gonna try and set everything up before i got to work tomorrow afternoon (sunday 12th) If i fail to check it out tomorrow I will keep you guys posted on what i find and if i fix i'll lte you guys know. Thanks for all the help!

 

OK, so I need to get a life... proven by the fact that I was thinking about your AC problem and am writing this at 7AM. LOL
A good point re checking the vacuum .... except I don't know how our C5 HVAC doors are controlled.... i.e. if vacuum or electric. Another simple test you can run ... feel the acculumulator (receiver/dryer) when functioning properly (after AC has stabilized -- meaning running for a few minutes) to know what and where it should be cold. When it fails, pull over, pop the hood, and check again. If cold as before, then problem is almost for sure with HVAC mixer doors OR fan motor or its circuit. If not cold, check to make sure the compressor is engaged -- it (the front-most part of the compressor clutch -- in front of the rotor (the part often called the pulley) should be spinning when engaged (demand for cooling.) If not spinning, it seems the prob is either electical/computer OR, that the hi-lo cutout is turning the system off, then allowing it to come back on after the system starts to equalize high and low side pressures. A clogged or paritally clogged orifice tube, evaporator, or condensor could cause this.
Two things you might want to do....
1. If you have an infra-red (non-contact) thermometer -- $20 - $40 at Harbor Freight or on Ebay,) you could point it the condenor (yeah, jack the front up, BLOCK IT AND PUT ON STANDS) and scan temps in direction (or opposite) to refrigerant flow. Any sudden (in close proximity) temp change other than at the orifice tube (or compressor, obviously) indicates a partial or complete system blockage. There should be no significant temp change across the accumulator -- if there is, it is blocked, likely by deterioration/saturation of the dessicant. Temps across the condensor should be highest where refrigerant enters it, and gradually come down as one moves toward the suction side.
2. Drive it with the manifold/guages, both high and low, hooked up. Pressures will fluctuate up and down as the radiator/condensor fans turn on and off / change speeds or when stopped/moving .... more air --> lower high AND low sides... with more noticable changes on the high side. Unless your guage hoses are only like 36", you will be able to lay the guages face down on the windshield so they are readable (or readable enough -- LOL) when driving. Tape the set to the windshield, and don't try to latch the hood... just lay it down gently. I would think this would give you substantial insight into what and when whatever is happening, is happening.
If you do evacuate your system, because the orifice tube is the most likely point of blockage) I would highly suggest that you replace the orifice tube (and the o-ring where the orifice is located (single bolt to remove, just in front of the accumulator.) BE SURE to put a wrench on the line fittings to counter the torque of loosening or tightening the bolt, to keep the line from twisting.) NAPA has the orifice tubes AND complete o-ring/seal kit for literally a few dollars each, and it is a quick and easy job. Be sure to lube the o-ring with a tad (that's just more than a smidgen, which in turn is only slightly more than a hair hahaha) of PAG oil. Again, NAPA has I think a 4 oz bottle for 5 or 10 dollars. Cheap and easy if you are going to pull down the system.
Replacing the orifice tube will also give you some idea of how much crap (that's a tecnical term used by HVAC professionals) is in your system. Mine looked just like Rocco's in the link I gave in my post to this thread, yesterday. My guess is that you will be veeeeeery surprised at how crudded up (a term derived from the Latin "crap") it is. I sure was!
In case you do decide to flush your system -- or part(s) of it -- and I say that because to flush the entire system you will likely need to remove the compressor to get at the low side-high side bolt at the back of the compressor -- let me give you the benefit of how I did it......
First, you shold know that Autozone "rents" flush kits, vacuum pumps, manifold/guage sets, etc. You pay full retail, then get your $$$ back when you return them. No other purchase is necessary. Call them to see if they have what you need in stock; if they don't, they will order it from another location -- and you will have it in a day or so, at no extra charge.
Second, there are 2 basic types of flush, oil-based (which Autozone does carry) at a cheap 10-ish dollars a quart, and solvent-based, which I don't know if Autozone carries, but I know that NAPA does. Latter is expensive, about $37 dollah as I recall. The solvent-based works much better, but d*mn its expensive.... So what I did, which seemed to work great, is get one quart of each type of flush, using the oil-based first. DO NOT FLUSH THE ACCUMULATOR. Remove it from the system, and quickly and carefully wipe any residual PAG oil from around the fittings (if real oily use some of the solvent based flush on a lint-free shop towel to remove.... do NOT use break cleaner, etc.) and use mylar packing tape (laid flat across the openings -- it will seal opening really well) to keep atmospheric humidity from entering and soaking the dessicant. Note: It is recommended by shops / mfgr's to replace the accumulator/ receiver dryer (and may be required to maintain warranty of a new compressor,) but it is not necessary unless system has been left open or accumulator is clogged (did you check for temp differentials across it?) Even with lots of crud in the system, you will likely find the accumulator inlet to be very clean -- meaning virtually no crud -- as it is just downside of the orifice tube, which traps almost all of the bad stuff. Besides, the surface area of the dessicant (and supporting screen) inside the accumulator is large-- like 6-8 sq. inches -- so a little bit of crud will have no effect.
I used about 4 or 5 oz (?) ounces each time, and then kept repeating. Multiple flushes with smaller quantities will yeild a cleaner sytem than one flush (for each tube/ part.) (Ask me and I'll explain the math!) Flush with some oil flush, let it sit for a few minutes (to give it time to loosen the crap) while you re-fill and re-charge the flush kit, repeat, etc. I think I also did it in reverse direction toward the end, but hey, I can't remember for sure -- use your own judgment. Put cardboard or other absorbent material under the area, and lots of paper towels, etc, at the out-flow of whatever you're cleaning, to catch most of the expelled oil and crud. After using the oil-based flush, I then repeated as to all components with the solvent-based flush.... with tons more of metal particles, AND THE OIL FLUSH, being expelled. The solvent will rapidly evaporate as you blow air through each component -- the oil flush will not. Oh- you WILL want to sudse and then pressure wash the right hand side of the engine compartment AFTER system is intact.
Always use new o-rings when re-assembling. Hope this helps someone!

 

Hi, below is a link to the thread that contains the post originally done by CF member Plasticfan. These are very good instructions on how to get the proper pressures. I believe that if you charge using these parameters you will get rid of the freeze problem, if that is your problem.
Good Luck
SEE BELOW go to post #11
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http://forums.corvetteforum.com/show....php?t=1817090

 

Well you sure did have a hell of alot of time on your hands and an open mind to remember let alone think of all of that. But the mornings are good for that. Well unfortunatly i have not gotten enough time to myself to go for a ride around town or anywhere for a straight hour. It does work fine otherwise. But i just have alot going on soo i need to put some time aside so that I can get this done. When i vacuumed down the system and replaced the dryer, i didnt even think to look to see if it was and oriface tube system i thought it have an expansion valve in it. I'm so used to seeing it, I just assume everything has it So you did put up a whole lot of info that i will use when i find the time. But this is a priority to me cuz i like it when everything works correctly! I really apriciate you going out of your way with all that time just for me lol

 

Thanks for the thanks. I've found that this forum (and to a lesser extent, the Z06 forum) has been incredibly helpful to me over the years. So i'm just trying to return the favor. There is info on here that one can't get anywhere else! And ya gotta love the how-to posts with pics. We ALL gotta help each other, and we do!

 

Ok, well first of all sorry it has been so long since ive checked back or made any progress. But i finally got a consecutive hour and a half driving done and it is not blowing from the defrost or by your feet so im sure that eliminates the vacuume issue. its still at the dash vent setting but its just hardly tricling out. and i did take notice that when you wlak awa from teh car for a like 20-30 min tops. there is a very large puddle of water underneath IMO larger than normal so i'm goign to get inside this squirel cage if i can and clean it out this weekend for sure and i will let you guys know how it goes. So again i will update and thanks for the help guys i really apriciate it

 

Hi, if the system is not blowing right from when you first turn it on, that leads to a blower circuit problem, or a clogged blower, or a seized blower bearing, SEE THE BELOW LINK
http://forums.corvetteforum.com/show....php?t=2092511
On the other hand if it is blowing at the start and stops after a while that would still lead to the freeze up theory,(low improper charge) and the large amount of water under the car at rest would confirm it, as the drain is clear and working ok the water is draining off the evaporator as the freeze is melting down, and draining out to the ground as it is supposed to do.
Good Luck