I have a 1988 Freightliner FLC. This weekend I am going to be changing the expansion valve, receiver dryer and the trinary switch. Also I will be flushing all the hoses, evaporator and condenser. Basically flushing everything except the replaced components and the compressor. Does anyone know how much freon should be in this system? Also how much oil should I add. Red Dot has a pretty good formula to follow for oil but not sure how much I should take off for residual oil in the compressor?
If you are doing a complete flush, i would suggest removing the compressor and draining into a measuring cup then you will know what it had. Then you can add that amount of new oil back in. You can also look up your compressor make and model to see how much oil it is supposed to have and how that compares to the amount you drained out. The two amounts should be fairly close
On one website it says my compessor should take 5 oz. That seems awfully high to me for a rotary piston pump.
Is that the axial piston compressor( sanden or sankyo)? 5oz seems a bit high but maybe not. I'm not home for a few days so i can't check my manuals. How much did you drain out?
I do not have the system open yet. I am wanting to do it this weekend but have all the information at hand so I can get this back together and be ready to go Monday. Attached is a link to the compressor. I am not sure if 5 oz is what it requires or just what it comes with. I cannot find anything anywhere on a 1988 FLC air conditioner capacities. I can find some info for an FLD of a newer model. It says the FLD takes 3 lb of freon and 9 oz of oil. I don't know how comparative that is to the FLC system. https://www.coolairparts.com/AC-COM...-43555075-488-45075-ABP-N83-304049Q-QP15-1168
It's actually pretty close but no two systems ever seem to be the same with Freightliner. From one to the next even in same years. You have to remember some info is with or without sleeper, with sleeper most are 4.6 lbs.-day cabs 3 lbs. IIRC
This truck has no sleeper. Even if did it wouldn't matter on this model. The flc's had two dans under the dash and one was ducted to the sleeper. It did not have a separate fan and evaporator in the sleeper. I think they started doing separate units when they went to the fld model but i could be wrong.
Bunk A/C was a spec option, could be ordered with or without. That option doesn't exist these days.
Some compressors have a dipstick. Although I am not sure if they had them in 1988. The trouble is that the instructions said you had to charge run the system normally and then evacuate it and see how much oil was in the compressor and make adjustments from there. There were different levels depending on how far off vertical the dipstick was mounted. It could also be completely horizontal in which case it was useless. Probably trivia but it might help you. I probably have a manual in my computer if this is the case. I believe Sanden SD series.
Well finally got all the parts so I tore into it today. Removed the evaporator coil and cleaned it up. Akso flushed it out. Cleaned heater core and washed the air box it all sets in. Reinstalled with new expansion valve. Flushed all the lines and condenser coil. Replaced the receiver dryer and and the trinary switch. Got it all back together and sucked it down for a good hour. Put 3lbs of freon and 6 oz of oil in it. So far it does not seem to cool any better than it did before. Mylow side pressure is aboit 10psi and high side us about 175 all at 85degrees outside air temperature. My damn fan runs all the time and wont shut off. The fan circuit in the trinary switch is open! Called freightliner and they say the fan circuit is supposed to be normally closed. My old switch that circuit is closed. Looks like I have a damn defective switch! Started raining its ass off before i could look into it further so I called it a day. Does my pressures at 85 degrees look right? 175 high side seems a little low. Maybe not?
You need to put a digital thermocouple thermometer on the liquid line that exits the condensor. I try to find some metal that is convenient and insulate it with some foam or something. You want the temperature of that line to be about 10 degrees less than what the high side pressure is indicating and that is your subcooling. It means the last few turns of the condensor are full of liquid that is getting a little extra cooling before it leaves. If it has a sight glass, this can also help, but the high accuracy thermometer is what tells the tale really.
That left the factory as an R12 system. Are you using R12 or 134? Conversions are hit and miss IME. Low side seems low and likely to freeze evaporator.
I agree the low side seems pretty low. I have not had a chance to get back at it. The evaporator was developing some ice but the air coming out of the vents dont seem real cold to me. I need to get a thermometer in the vent and check it. It also had occurred to me that it just may be a system that does not convert well to 134 from r12. Being an 88 model it had to be factory r12. If thats the case it may be a waste of time and money better spent on a red dot back wall unit! New expansion valve, new reciever dryer, new trinary switch which is fkn defective! All the lines are good and i know the evaporator is not plugged. Despite the trinary switch it should blow cold as all get out. Only thing left is the condenser which dies not look Stellar! And the compressor which i have a hard time believing it would be bad if it will pump 175psi and pull down to 10 psi.
I dont know im following you. Are you saying if my high side pressure Is 175 then my condenser outlet should be about 165 degrees? I dont know what temp uts at but its just luke warm to the touch. Really so is the inlet!
Download a pressure/temperature chart. But there should also be a temp scale on your high side gauge. If the pressure is 175, then the saturation temperature (the majority of the condenser) should be 121 F. 10 degrees of subcool and the liquid leaving the cond should be 111F. So get the system running with the cab a reasonable temperature on recirc full fan, get the fan clutch on, RPM at 1100 or so and add charge slowly until your subcool is about 10F. This is the gold standard for charging if the calibrated weight is not available, or if they got it wrong. It would be nice if they had sold you a 134A ex valve. Usually that's what you get these days. As for freezing, there should be a temp probe hooked to a switch to disengage the compressor temporarily as the evap gets below freezing. Usually this only happens on lower fan speeds. It sounds like you need to add charge but I always do it by the subcool method, it is directly measuring what you need to be measuring, but it needs a thermocouple, no point and shoot thermometer for me on this one.
Ok I think I get what you are saying. The valve they sold me when I look up the part number does show it to be a 134a valve. From what I see of the chart I am probably low on charge. I have already put 3 lbs in this system. 4 12oz cans. I didn't get a soec from freightliner as this truck is old and no one there seems to know or how to find out for sure! I have a hard time believing it would take more than 3 lbs but I suppose it could. I need to solve my trinary switch issue before I add more freon. I am going to have to pull the system down to replace the defective new part! Its the kind that does not have a Schrader valve! Also i think when I pull it down I need to go ahead and change my condenser. The find are fairly well screwed. I used a fin comb but it's still pretty ugly.
Replacing the condensor good. Hope you don't regret leaving the compressor, if it fails it is going to blow chunks into the new condensor. The idea with the subcool method is to be able to measure when the bottom of the condensor is starting to get full of liquid. And then add a bit more until you have some excess liquid down there. The numbers tell the story as it goes. When you do it this way you know it is right. But I prefer to do the measurements under the right conditions, cab 80-90F recirculate windows mostly closed (so it does not suck in hot engine air from the cowl), ambient temp 90F or better (so it's a good test but not so hot I'll melt standing next to the engine), fan locked on, engine at medium speed, and supply air to the condensor that is not getting recirculated from the radiator or engine however that works out for you. Sometimes nose into the wind, sometimes a big fan or sometimes nothing at all.
Yea toast!
I just hate shot gunning part I dont know are bad. I guess from a preventative standpoint you are probably right since the condensor Is $309 aftermarket and $585 from freightliner! The compressor is only$207 from freightliner!
Every system I have either resurrected from the dead or known of someone else doing the same, usually regrets not replacing the compressor at least, if it sat with air and nasty oil in it for years. That condensor does not look so bad from the picture, but I don't know if a new one will be better for 134a
Its not a resurrection. I been running it the last two years. Air never was great from when i got the truck. Looks like someone recently replaced the compressor and the evaporator coils before i got it.
Ok update. After chasing down my large drain pan from the terd i loaned it to that NEVER returns tools i got my oil changed and was able to run this system a bit. As it stands its 86 degrees outside temp. I am getting 60 degrees at the vents. I replaced all the vent louvers today so the damn thing would stay open and you wouldn't have to wedge cardboard in them! Now they stay open and im getting good airflow. I also had an idea of using some plastic to create a drip ledge so condensation drips into the drain pan and not down the cover and onto the floor. So far nice dry floor which is excellent! I then also moved tje cool switch probe a little farther away from the evaporator coil inlet. Added in the missing fan that goes on the spot for the sleeper air. Then wired it to come on in unison with the dash fan. For rigjt now it just blows out into the cab. The added airflow did seem to help keep the coil from freezing and it also increased my pressures. Ok so performance numbers are: Condenser inlet 105° @ 200psi Condenser outlet 85° evaporator outlet 41° @ 20psi 86 ambient temperature Seems odd id be loosing 20 degrees from the evaporator to the vent as short of a distance as it is? I think given the numbers im probably low on freon charge. I think another problem I may be fighting is this old freightliner cab is about as insulated as a beer can without a cozy in a forest fire! Plus it leaks air about like a 1957 chevy with the top down! I think from here i need to wait for my new trinary switch to come in and i can change it and get that issue resolved and then try and do a proper charge
Ok so I been setting here all afternoon thinking about this and what you said. Here are my performance numbers. condenser inlet 105° @ 200psi high side condenser outlet 85° evaporator outlet 41° @ 20psi low side 86 ambient temperature Ok so if I go by what your saying i have a temperature drop across my condensor coils of 20°. I think what your saying is I want to achieve a droo of 10° which would be prime sub cooling? So given that my high and low side gauges are low and my sub cooling is 20° The only conclusion I can draw no matter how many times i beat it is that im low on freon charge. I already have 3 lbs in the system which seems max to me. I just cannot get over that it would take more. I remember what you said aboit some trucks with sleepers taking 4 lbs or more. This truck had a sleeper on it originally. It has been converted to a daycab. The sleeper did not have a stand alone evaporator coil separate from the cab evaporator. It had two fans on the cab mounted evaporator under the dash. One fan was ducted to the sleeper. All the ducting is still there but just dead ends at the back wall! Ok with all that being said the evaporator is quite large. Its about 21 inches long and about 8 to 9 inches wide and two inches thick. When I think about it it is much larger than the fld which has a sleeper mounted evaporator unit. i guess im just gona have to get it in my head how large this system is and that it is gona take more than 3 lbs which is spec for a daycab fld. Unfortunately i just cannot find any information on the old flc system from freightliner or any old knowledge from anyone experienced on that exact model truck. What's your thoughts on where i need to go on this?
That's what I was saying above-not all systems were the same. Especially if there was a design change in mid year and Freightliner is known for that. It's kind of like a clutch adjust till it works sometimes.
I just wish I could find the service information as per my vin number. Unfortunately I am left with such a guessing game! I guess i just have to belive what the gauges and temp readings are showing and go by that! Any other ideas?
Oh also i looked at my other 3 flc trucks and they all are set up same way as this one! Hard to believe there isnt someone out there that would know as this truck does not seem to be an odd ball when compared to my other 3 trucks! Nice to have other for comparison. Around here we call that an arkansas blue print lol!
No, to get sub cooling you calculate the temperature you should be getting based on your high side https://www.igasusa.com/pt-charts/R134A-PT-Chart.pdf So if you have 200 psi your saturated temperature is 130 degrees. Now if you are measuring 120 degrees at the cond outlet, you have 10 degrees of subcool. I think you are quite low on charge also. But with an unknown charge amount, you need to sneak up on it so as not to overfill. Also after adding freon, wait a minute for readings to stabilize.
Now for the reality-didn't want to say this but a Freightliner HVAC system was know as {Freeze or Fry}. Maybe one in ten worked out by the numbers. Freightliners were known for poor cab heating and cooling system. Especially the earlier models. It's only been in the last few years that Freightliner has been able to produce a reliable system. The old classic cab which you have had many issues with the dash controls and ducting, plus freon leaks. Even though it should work just like any other system those were problematic, I have dealt with them for years if you get it to put out just decent cool air be happy with that. You could chase it till the cows come home.
Thats kinda why I dont want to throw a bunch of money at it. If I cannot get it to a point where it will work well without a bunch of expense then next spring its going to be sporting a brand new nuts to buts Red Dot back wall system! I think it would be money better spent if its gona get expensive! Probably the direction I should be going any way but i figured id give it a shot! Unfortunately in my old age just being happy with something barely ok just is not an option anymore
Truck shop have you ever seen anyone tear this crappy plastic dash out and make a custom metal dash kind of like an old school Peterbilt or Kenworth metal dash? Seriously been thinking about it. This Freightliner dash is the worst. I may try it on one of my other trucks when I do a dump truck build!
Nope never seen anyone do that. It could be done I suppose but is it really worth the expense and time? Those cabs were troublesome from day one. Installing dash valves is a real delight. Freightliner cut the hoses short so when each one is disconnected it disappears into the darkness and depths of the dash. Poof gone.
Yea i have said a few choice words just getting the panel out far enough to get a wrench on the fittings let alone even see what your working on!
Is your heater door closing completely and is your heater hose valve closed completely? The dash is hung on the firewall with 4? plastic hangers that will break. IIRC they are no longer available from Freightliner. If your dash shakes, the hangers are probably broken. Does your receiver dryer have a sight glass? IME conversions will work better with some bubbles in the sight glass.
There's more hangers than that, The big problem is the air operated heater door valves-obsolete. can't be gotten.
This system does not have a hot cold blend door. The heater core is stacked directly above the evaporator coil. Only door that would have any effect on this system is the fresh air recirculation door. Yes its operational and seals good. Not only is the heater valve new and completely shut off but the valves at the engine are shut off as well. For some reason the new receiver dryer that Freightliner lists as the part number needed does not come with a window like the old one did!
Not sure what valve you're talking about and I don't believe I have that valve in my system. However all the valves in this system that Freightliner said was obsolete cannot get we're all made by Humphreys and can still be gotten from them or on the Internet. Basically they are obsolete in the freightliner parts system only. I think I even did a thread on those valves when I replaced the one on mine that is a little push button valve that gets activated when the temperature lever or the dash defrost lever swings over and pushes it in.
Sometimes they put a piece of tape over the window and paint the whole thing black, and you have to peel it off. However, window or not, the subcool method works 100% of the time on a TXV system.
No these connect to the heater doors.
Damn this system is really giving me a fit! It shouldn't be this damn hard as its a pretty damn simple system. So wed had the high pressure line from the pump to the condensor coils fail. The aluminum 90 degree elbow on the compressor decided it has spent to many years as a freightliner part and wants to be reborn into something else! So got new hose. Then my new trinary valve showed up. Took my multimeter in with me when i went to pick it up and surprise surprise its the wrong damn one! Guess the parts guy thought I was kidding when i said i needed nc on fan circuit and he assured me that it was! Yea he was wrong! Add in ron white voice with that last statement! Ok so finally they got it in thier fkn head the computer is wrong and we dug out the old dusty alliance books and got the right damn part number! Dont have it will be here tomorrow. Of course they were wrong on that also! So Saturday morning frantic seach now rhat i had the correct number and managed to find the single last one in existence in Springfield mo at fleetpride! By then i was hot tired annoyed and said screw it i will finish it sunday! Ok sunday sunday sunday. Put on new hose. Put on new trinary switch. Evacuated the system and started to charge. Now for some reason my compressor pulls down so slow it will hardly pull the freon in. got about 2 cans in. The high side will go up to about 175 . If you crack the low side valve open on the can it will go up to can pressure. close the valve and it will suck down to 10 psi but takes several minutes to get there. I think I must conclude that my compressor is sub optimal and needs replaced. Expansion valve is new and i think if it was stuck open it wouldn't allow the compressor to pull down that low. Also the high side pressure would be lower i would think. Gotta be the compressor. Odd it would be worse now than the first time I charged it after a system flush. Any thoughts?
I think you may have been better off and $$ ahead just putting in a red dot. Since we're past labor day, I'd like to think we are out of the hot weather, but who knows. I totally rebuilt a factory a/c system last year, and it didn't work right either. I should have just gone aftermarket and been done with it.
Yes and no. Im really not that far into it with the expansion valve, receiver dryer and trinary switch. A little over $100. Well within gambling range. The hose id have to get even if I get the red dot unit. Same way with the compressor. As it stands all i need to order for the red dot unit is the in the cab part of it. No need to buy the complete system as the rest will be new. All i will be out is a expansion valve really! The red dot unit is looking better every day!