1988 FL freightliner air conditioning q1

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

Birken Vogt said:

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

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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

Birken Vogt said:

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.

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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.

Truck Shop said:

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.

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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?

Truck Shop said:

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.

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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!

workshoprat92 said:

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?

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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.

Truck Shop said:

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.

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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.

Truck Shop said:

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.

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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.

terex herder said:

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.

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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!

Truck Shop said:

There's more hangers than that, The big problem is the air operated heater door valves-obsolete. can't be gotten.

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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.

workshoprat92 said:

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!

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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?