Hey hef I got a redot a/c unit a134 roof mounted . I have a restriction can't find it. Have changed everything but hoses until tomorrow. Condenser evaporator expansion valve 2 driers and compressor 75 degree air temp high side 200 low side 15 2.3lb charge what manufacturer calls for. We are putting new hoses on it tomorrow but I'm not seeing and cold or hot spots in the lines anywhere. Line coming out of expansion vavke will drop down to 55 degrees and almost 100 degrees line going into expansion valve.
So, what about your condenser? Do you have air flow across it. With a roof unit, does that mean no fan for the condenser?
Low side @ 15psi with engine idling sounds like undercharged. What started all the throwing parts at it? My experience with reddot leads me to believe that the expansion valve comes in different ratings in the same configurations. Could you have put in the wrong one?
I would have thought just the opposite . Good air across the condenser at idle we should be like 0-5psi on low and maybe 125 on the high. It sounds like overcharge to me. Maybe even inadequate vacuum prior to charging.
Have you flushed or at least blown compressed air through any of your lines.? At 75 degrees ambient, 200 seems high and 15 is low.
I blew through whole system piece by not a single piece of debris was found at least 30 min vac down each time. First trip topped system off. Diagnosed restriction ordered expansion valve and drier... Charge system same 15 and 200 tried over charging just made difference worse. Went over system with non contact thermo couldn't find a hot spot or cold spot rolled dice on condenser internally contaminated same.... Ordered a new evaporator and another drier Same results.... Today tried swamping expansion valve from a Kenworth the customer had on shelf that is a 4.lb system. It made it worse low side is about 10 psi. Now getting new hoses made tomorrow and we put a new compressor on somewhere in between because after all this we don't want that to go bad. It's a Timco 425 feller buncher maybe the dealer sent us a wrong expansion valve? Idk but it's sure is my worst a/c job to date.
Those pressures sound normal to me at 75 degrees. You are going to need to measure temperatures more certainly before we can tell exactly what is going on. To start we need to know what the temperature of the cold liquid refrigerant leaving the TXV is and what it is coming back as vapor to the top. This will need to be done with thermocouples and insulation, a point and shoot will not be very accurate but might get somewhere. Also what is the temperature of the liquid once it leaves the condenser at 200 psi once it gets out of the area of the cooling fans. Is the clutch cycling when you are doing all this? You should have the temperature switch bypassed on and preferably do it on a warmer day. Is there full air flow going THROUGH the evaporator, not around it? Sticks of foam pipe insulation can help with this.
Are you charging by weight or by performance. I would pull some air across the condenser and check to see if your pressures drop and performance increases. Just got treed by BV, solid info. I keep asking. Is there a fan blowing or pulling air across the condenser? Is it tied into the trinary switch ?
Oh, btw what kind of expansion valve do you have? The block manifold or the one with the disc and capillary tube? If capillary style, do you have the bulb secured to the outlet tube of the evap coil and properly insulated?
Twin fans moving lots of air across condenser panel I charged this both ways with a scale and by performance. With point and shoot condenser inlest 120s out about 100 line going into expansion valve 70s and 50s coming out with the tiniest amount of Frost on discharge from expansion valve.
Block style expansion like ones pictured above
Or spray it with a garden hose, quick and easy. But at 200 psi I don't see how there is much to be gained. Also I forgot to ask is there a sight glass to see if there is solid liquid or bubbles going to the evaporator. Edit: I looked at the chart and 200 is too high for the condenser after all especially at 75 ambient. Correct my understanding if wrong but you are seeing 200 condenser pressure and 100 degrees outlet that is 31 degrees of subcool, indicates overcharge but a garden hose will take care of that temporarily.
There's no chance that the oil charge is too much , is there? Do the fans run continuously? Or tied through trinary switch? If they're continuous, you're losing air flow across the condenser . That pressure is too high for a cooled condenser. That and you're only shedding 20*.
I know I beat the condenser thing to death. I do that for a reason. Every challenging A/C problem I've encountered and sometimes overheating as well has been tied to poor air flow. Either dams are missing, fans bolted to hubs backwards... all kinds of crap. Once pulled a perfect blanket of cottonweed off a radiator face. Since it was between the CAC and the rad, no one saw it . I know that's not what you have, but the principle is the same. Place a rag in front of or behind the condenser will the fans hold the rag against the face? Do they blow through the condenser/ housing or around it. Does the air flow forcefully blow the rag away at the exit side of the condenser? BV was spot on with the garden hose. I completely forgot about that as an option. The liquid water on the surface of the evaporator will drop pressures like a rock. If this simple test proves out, you gotta look at airflow
What is the temp at the line going into the evap core? Is the heater shutting off properly or adding heat to the system?
Condenser has alot of air moving across it and it pushes alot of heat off it very warm air. Didn't try watering it down when I was there. Line going into expansion valve witch is mounted to evaporator is in the 70s can't get to evaporator with system operating. The heater hoses are shut off and there is no coolant in the lines at heater box.
Well your diagnosis is textbook correct with an obstruction based on the pressures that you have. However I still struggle with that thought process since you don't have a sudden temperature drop or a frost spot anywhere along the system. I was really hoping that we would find something with poor air flow across the condenser to drop your in your Inlet pressure that doesn't seem to be the case I am all out of ideas I apologize I could not be of more help
With the H-block TXV, the TXV opens and closes to maintain the superheat at whatever it is set for. Like the one in the picture is 5 degrees superheat. So if the low side pressure is 15 psi, the vaporizing liquid leaving the TXV entering the evaporator should be 15 degrees F and the vapor coming out the top of the evap, back to the TXV should be 20 degrees F. If I understand the problem correctly, the evaporator outlet is more like 50? If this is the case the evaporator is not getting enough refrigerant and you already know to look for cold spots to find the problem. Does it have a sight glass? In any case I would be using thermocouples taped to the pipes and insulated from the outside air at this point. I would be measuring evaporator inlet, evaporator outlet and condenser outlet temperatures.
Thanks for the help I really appreciate the descussion I'm not the most technical with a/c yet. As far thermo couplers do you mean the type to a multi meter if you can post a link or a pic I'm interested in getting some. My customer is getting a local radiator shop owner that is a Reddot dealer out next Tuesday to shed some light. I will be there sucking up whatever I can from the guy. I will report back when I know more.
This is what I use since I didn't buy a meter that already had the setting on it https://www.flukeonlinestore.com/products/temperature/80tk-thermocouple-module The trouble with measuring lines and hoses with a point and shoot is that the outside of the line will be affected by all the ambient air the engine fan is throwing around. But if you tape a thermocouple to the line in question and then insulate it with some foam rubber or even a wad of paper towel or a rag then the surface of the hose or line will quickly be the same as the fluid inside and then you can get a good idea what is going on. Good for thermostat diagnosis and air conditioning.
Is the compressor cycling or just staying on? I’m curious as to what the pressures do when the comp. cycles. Also, I did an a/c job on a Volvo loader a while back. The book calls for about a 4 lb charge. When I put 4 lbs in it my pressures spiked and it wouldn’t cool. Everything else checked out but for whatever reason 3 lbs was the magic number on that particular machine.
Compressor doesn't really cycle much when it does pressures start to neutralize normalish speed ? Vent temp is 60s. I have charged by performance if I under charge it almost looks promising (like itilow on charge) if I over charge works good when ambient temperature is 60s and low 70s. The red dot guy says the pressures aren't whole issue. Idk if the expansion valve is working and condessor has lots of air flow why won't the expansion valve get cold? I've got like 40 hours between working on machine and travel time. I can't bill all that so now I'm loosing money and having to admit Im in over in over my head puts this job is number one on getting off the list. I feel I have a decent understanding of a/c but just not the experience diagnosing. At least being out of comfort zone usallus leads to learning..... Thanks for all the discussion can't wait to get some temp probes and give the water on condenser a try.
I am not a tech but I have installed and trouble shot my own system.... Does it have an inline filter or an orifice tube... I do realize no orifice tube is used on a expansion valve/receiver-drier set up unless it is a dual setup. I would feel the lines near the compressor, use your hands. Is one cold? Is it running... 200 psi does not seem high enough.. low in these temps? I would have thought it should be higher.. Is the belt tight on the compressor pulley? Is the compressor cycling, if so why does it turn off? High pressure low pressure... garbage compressor? Maybe your termostat sensor has vibrated loose from the evaporator cooling fins or maybe it is too close and touching? I installed a complete system and did not realize it had a cut off/on sensor (thermostat) inside the case, sealed it all up and could not figure out why it would not call for the compressor to cut on... cost me 2 days and had to cut it all back apart... Is water forming on the evaporator? From what i learned working on my own... it came done to the temp sensor on the fins too far off and it would freeze, to close and it would not get cold enough... and a fan on the condenser... used gauges as a base line but charge was utimately based on max system cooling based on temp out of vents and hose temps... Condenser needs to be on a certain angle to correctly accept charge.. It should cool with out a fan but the fan should help drop the temps by 10 to 15*, I installed one on a relay controlled by compressor call voltage... worked like a charm and it was an add on.... How does a blockage occur on a system unless you have a major part failure it is a closed system... Your expansion value might be wrong the machines use the heavy duty type (block type as fun with fuel stated?) not the cheaper light duty automotive type ... At least thats what was on my case.... I bet it is a real pain trying to find the gremlin in the field. I don't believe I could have done it. Took me more than a week to install and another few days to trouble shoot all my issues.. Tell them its time to ship it you so that you can properly trouble shoot it... Bet they dont like that...
Debris and contaminates internal can come from compressor, lines, drier, orfice tube expansion valve external possiblity s are endless lol this never work right since customer got machine always works at low ambient temperature never above 80.
That is kind of what I thought at first but he is low ambient, 75 or so, so 200 would be quite high actually. But really you need to have a thermocouple on the liquid out of the condenser to know for sure whether it is high or not. 15 psi low side is quite low, normally it would be 28-30 or clutch cycling regularly to keep from freezing. High high side and low low side generally means restriction, but it should get cold where the restriction is located. I want to see how this one turns out, sorry for the OP's wasted time.
I bet it is a real pain trying to find the gremlin in the field. I don't believe I could have done it. Took me more than a week to install and another few days to trouble shoot all my issues.. Tell them its time to ship it you so that you can properly trouble shoot it... Bet they dont like that...
Here's something I left out those pressures are at idle the press difference increasing as rpms are raised. Thermal couplings and a log book of temperatures would be super helpful at this time. There is a guy coming out on Tuesday so I'll post that night.
I think i would do it at operating rpm.. or maybe 1800 rpm I think i read somewhere you must check the system at operating rpm... not at idle..
200 at idle with fans blowing hard and maintaining 15 on the low. I think you were onto something by reducing the charge. Under those conditions, I would want to see 0-5 psi on low and 150-130 on high. The fact that you're up to 200 and 15 .... just seems too high to me with the condenser fans running. Sorry to hear you're taking such a beating on this.
Don't be sorry guys its a business can't win them all my dad always says education is expensive one way or another....
You keep saying 0-5 psi low side, you mean with the freeze switch locked out correct? I would never expect to see it that low in an operating system, the evap would freeze to ice in no time. I always try to troubleshoot AC between 85 and 95 degrees outside temp, 85 because anything lower is meaningless and no challenge to the system, 95 because pressures start to get unreasonable and bad things can happen to your gauges (ask me how I know) If it is a truck I will lock the fan on and set engine RPM to 1300 or 1500, ear protection required. But engine RPM must be middle to high regardless of truck or machine or car. If it is a car then some means of providing air flow must be provided, sometimes I even drive with the gauges stuck in the window. Of course on a Red Dot system you have a rooftop with electric fans, no problem there. As for the interior, recirculated air with the doors/windows open to get a decent amount of warm outside air but not too much hot air and definitely do not want to get any hot air off the engine/radiators.
Check to make sure the pressure line from the compressor goes to the top of the condenser, ran into this once on a red dot system with the separate condenser unit where the inlet and outlet hoses were the same size in side the box and hooked up backwards. Also make sure the drier is installed in the correct flow direction . And as mentioned before too much oil in the system will not leave enough room for the correct freon charge and will make head pressure spike with the correct charge. Flow should go through condenser then the drier
Sorry about late reply been busy this ended up being the box had a panel missing blower was pulling warm air from out side..... The red dot guy checked my worked saw condenser was getting cold and left.... Later I found small panel missing it was a nightmare job. I really missed that one thanks for all the help I learned alot about a/c performance on this one