Air conditioning - pressure switch bad? April 21, 2009, 11:31:44 PM Edit:I think I'm attempting to charge the system too quickly. I assume I should go ahead and force the compressor to turn on to help build the pressure up quicker.How is the high pressure and low connected? Would pulling vacuum on the low pressure side cause vacuum on the high or does the compressor and orifice hose keep the two sides completely separate? I think I need to re-pull vacuum on both sides and recharge at 35psi low pressure again.Also the system's oil is supposed to stay in the system after pulling vacuum, correct? I should probably add like 1-2oz if it hasn't been drained out? Quote Selected
Air conditioning - pressure switch bad? Reply #1 – April 22, 2009, 12:29:45 AM Not 100% on the question in there but here goes. What is going on? You charged the system but the compressor not coming on? Yes vac'ing down the low side does the compressor and high side. It is to suck stuff out but also check to see if it holds that vacuum for 30min to and hour to double check for leaks. Yes some oil will stay in there best to keep track of how much comes out if you can. Then charge it up. But if you have already charged it. Take a pressure reading on both the low and the high side. Find out if you have the right pressures or no pressure on the high side. If you have the right pressure or close I would jump the pressure switch and see if it gets cold. If you don't have pressure or real close to the right pressure on the high side. Something is wrong and plugged up in there. Did you install a new orifice tube? If not and you have the factory hoses you have to cut the metal tube and install a new section with new orifice tube. Most auto parts stores can get you a kit for this. Also if your installing R134 and gonna replace the orifice tube get the auto adjustable model. It will adjust to what the motor is doing to make the motor work best at idle and higher rpm's. I didn't do this and at idle at a stop light it starts to get warmer quickly. I'm told part is due to the orifice tube and part due to the r12 condenser not having near the fin count as the R134 style. So install a newer R134 style condenser or mount a large electric fan on the front of the R12 unit that you can turn on in town.hope this helpsStuckman Quote Selected
Air conditioning - pressure switch bad? Reply #2 – April 22, 2009, 12:49:54 AM My system was taken apart and capped off when we had to do the heatercore last year, being reconnected after the swap was done hours later. It's been dry since but not much oil came out with the rest of the system when this was done.New lines, compressor, orifice rube, and accumulator were installed 2-3 years ago, and condenser/evaporator cleaned out, after being a/c-less for 10+ years. The swap was done with conversion parts and fresh oil. The system ran good at that point in time and is still leak free. I'm just not sure if me only pulling vacuum on the low side earlier also did the high side. If not, I have to redo it, otherwise I just need to continue where I had to leave off today due to it getting dark.I'm just looking to get the a/c back up and running. With my vacuum pump, I've got that parts set , along with all the gauges and such, I just need to know if pulling vacuum on the low side created vacuum on the high and get an idea on how much oil I should add back in. The latter may not be something I can get from you guys. I would think that without vacuum though, the oil would also come out but I get nothing but air coming out of it. Quote Selected
Air conditioning - pressure switch bad? Reply #3 – April 22, 2009, 08:30:53 AM Your lack of oil coming out during the vac'ing process isn't nothing major. That oil likes to stay in the compressor. To get it out you would need to take it off and drain it. Then if no oil came out then you need to put little if any in there. And yes when you pull vacuum on the low side it does both sides and the compressor. Quote Selected
Air conditioning - pressure switch bad? Reply #4 – April 22, 2009, 08:43:44 AM Quote from: Seek;268548 I just need to know if pulling vacuum on the low side created vacuum on the high and get an idea on how much oil I should add back in. The latter may not be something I can get from you guys. .this question bugged me a few years ago and so i made a few observations and asked a few questions.the correct answer to how much oil will be "refer to the maker of your compressor",,yeah right.Most any real good compressor has a sight glass on the side. our compressors sit sideways and any good compressor I have seen on larger diesel engines and such have a sight glass. Its location is approx 1/4 to 1/3 of the way up from the bottom. The sight glass should show the oil pretty much dead middle.I looked at many good compressors of various sizes and noticed the sight glass is oriented at the same location.My conclusion what that you fill the compressor about 1/3 of teh way full. when the pump kicks on, the oil level will drop because a lot of it will coat all your interior lines. The length of the line on some applications could be as much as 60 loop feet.there is a pretty good bit of math involved when compensating for line lenght. ours are probably only 10loop feet so that would be the amount of line that gets coated.Too much oil and your compressor locks up because the oil expands, too little and it does not lubricate.I asked many good hvac guys this one question and most of them pretty much agreed.> " in general, isnt it true that a typical compressor needs to be about 1/4 - 1/3 the way full of PEG oil staring with an empty system?". Typical answer was ,,"well, closer to 1/4 of the way full with a dry system but that all depends on the line length".so if you fill the compressor completely and manage how many cc's were put in, empty back out 3/4 of that and you have a good start. With dry lines, it puts you at an oil level closer to 1/4 full. To be honest, no one is going to give more straight of an answer. I am just sharing what i have observed.Take a look at some big rig engines and eyeball thier compressor, you might see the sight glass im talking about.once you get the oil in, pulling vac and charge is easy.getting nothing but air out now (ie- r12 or 134) is normal. If i hit the purge valve and got oil, I would know i just found my problem,, too much oil. Quote Selected
Air conditioning - pressure switch bad? Reply #5 – April 22, 2009, 08:56:42 AM Sounds good - I have a compressor from ackits.com that I believe was new - don't remember seeing a sight glass but it may be there... Quote Selected
Air conditioning - pressure switch bad? Reply #6 – April 22, 2009, 09:10:33 AM you could in theory jumper the presure switch connector to keep the compressor on,, with the right amount of oil, its just going to get purdy hot. Quote Selected
Air conditioning - pressure switch bad? Reply #7 – April 22, 2009, 12:46:29 PM The AC system is just a large loop, evacuating low also takes care of the high or vice versa... Lemme know if you find a sight glass, I've never seen one on any newer system later than the early '80s... Quote Selected
Air conditioning - pressure switch bad? Reply #8 – April 22, 2009, 01:39:26 PM Quote from: jcassity;268578you could in theory jumper the presure switch connector to keep the compressor on,, with the right amount of oil, its just going to get purdy hot.I would more than likely run jumper wires over to the gauge so I could turn it on and off myself so I can keep adjusting the valve. Quote Selected
Air conditioning - pressure switch bad? Reply #9 – April 22, 2009, 10:33:50 PM None of this is working - what part is bad? I tried a different approach that seems to be getting me into the same trouble. With the car off, I again pulled vacuum on the system, cut it off, connected a canister, purged the air in the fill line, then filled the high pressure side with the canister upside down. As it stopped filling, I closed the valves, purged the fill line again or liquid, then opened the canister and purged air from the fill line and started the car. Before I even had a chance to open up the low pressure line, the compressor cycled a couple times before coming to a screeching halt and not running anymore. Jumping it wouldn't turn the compressor. It is acting like I have liquid in the low pressure side but I've only put refrigerant into the high pressure side so far. Both are reading ~50psi. I had this problem with the compressor earlier filling from only the low pressure side with the canister upright so I figured I'd pull vacuum and try over again.During this time, filling the high pressure made the low pressure eventually ease up to 45psi by the time the car was started. It dropped to 35psi on the first couple cycles and then stopped altogether.Does this mean I have a bad orifice tube? Compressor's just shot? It's getting 12v when I manually jump it but the thing is locked up hard and the clutch can't engage. Earlier prior to this attempt, it kept cycling between 25-48psi (on at 48, off at 25) but the high pressure would never build more than 60-70. Manually running the compressor it would run continuously but the low pressure never went below 40psi and the high pressure wasn't going anywhere over 50. I found this extremely odd. The clutch should be fine, it just can't go in after it hits a certain amount of refrigerant in the system. Quote Selected
Air conditioning - pressure switch bad? Reply #10 – April 22, 2009, 11:34:23 PM Quit worrying about high vs low, should always charge from low side, like I said before, the AC system is just a big loop... If it's locking up after charging only a pound or so you likely have a blockage, probably the expansion valve(orifice tube) has crud in it...BTW what's the air temps??? If it's below 55* or so, evacuation may not boil all the moisture out of the system and the orifice is freezing... Quote Selected
Air conditioning - pressure switch bad? Reply #11 – April 23, 2009, 12:00:02 AM 75ºF.So should I not worry about being able to see refrigerant as long as the can is up right? I've tried to keep the pressure relatively low to help prevent more than gas from escaping the can.If the compressor's cycling then it should be fine? I'm not sure how the compressor itself separates the high and low pressure sides and if anything can leak by. I guess I should replace the orifice tube which means again replacing the accumulator also.Edit:If there is a blockage, shouldn't the high pressure side increase if there's plenty of r134 in the low pressure side? Everything I've read about blockages is causing extremely high pressures when running. I seem to have an equalized system that won't compress a thing. Quote Selected
Air conditioning - pressure switch bad? Reply #12 – April 23, 2009, 06:31:02 AM Uhhhh... Yes if there's a blockage the HS pressure should be extreme... Guess I was getting sleepy when I made that post...Internally the compressor is similar to a engine, pulls in on the low(intake) and pushes out on high(exhaust)side... Yes there is pressure on both sides, but the high is always trying to equalize the system by flowing to the low... There are valves(probably reeds) internally that block the flow from reversing... Those components can be defective and keep the compressor from pumping at all, but I've never seen one lock because of this... Possibly it's not locking at all and you have a defective clutch(only partially engaging)??? How does it act with a straight 12V applied??? I had one with a defective pressure switch, that had internal resistance and would only weakly engage the clutch... Worked fine idling, but caused the clutch to slip at higher RPMs(when I drove it), thing like to have drove me crazy...Quote from: Seek;268727Does this mean I have a bad orifice tube? Compressor's just shot? It's getting 12v when I manually jump it but the thing is locked up hard and the clutch can't engage. Earlier prior to this attempt, it kept cycling between 25-48psi (on at 48, off at 25) but the high pressure would never build more than 60-70. Manually running the compressor it would run continuously but the low pressure never went below 40psi and the high pressure wasn't going anywhere over 50. I found this extremely odd. The clutch should be fine, it just can't go in after it hits a certain amount of refrigerant in the system.Just reread your posts and if you aren't building HS pressure, compressor may be defective... Unfortunately the orifice tube can act similar... The orifice is the point where high vs low meet and is basically a metering device... It causes the refrigerant to "dam up" and slowly enter(expand) into the accumulator then enters into the evaporator... This expansion is what provides the cooling(same as cranking open the valve on a can and dumping it into the atmosphere)... If the orifice isn't providing metering, the system pressures will be close to equal(lo vs hi) and due to no expansion of the refrigerant, you'll get no cooling... Quote Selected
Air conditioning - pressure switch bad? Reply #13 – April 23, 2009, 08:57:28 AM When I have low pressure in the entire system, jumping the compressor clutch would spin continuously but the low side pressure was never decreasing (against what was happening with the cycling where it would decrease on the low side and build for a second on the high before cycling off). I'm seeing weird behavior so something's gotta be off but due to the slow nature of the high and low sides equalizing, something's gotta be working also. I'm assuming the compressor is messed up. Quote Selected
Air conditioning - pressure switch bad? Reply #14 – April 24, 2009, 08:41:22 PM So I had a shop look at it and before they even looked at one important fact, they did some diagnosis on the system. After realizing it's running r134, they stopped and told me so. No charge, but they think that there's a blockage, even with the lack of high pressure. Soooo, I guess I'll pull the system apart at the condenserand gas line and check for blockages. I figure if I'm doing this, I may as well replace the condenser.Has anyone tried installing a larger condenser, namely a 97-98 Cobra one? It appears that besides mounting brackets, it should go right in. Also what company should I trust for this part? It's high pressure so I don't want something that'll rip open. Quote Selected
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