A/C Problem. HELP!

Thrmo. under dash in heater box bad makes A/C comp, cut off to allow it to thaw out an blow cold, 4 screws to it up an replace it

 

4 cans is not enough freon for a semi.

1 can of charge is not enough for the compressor.

you need to actually put in the oil. not use a charge can. you need to read the instructions for how many ounces oil it takes. the mechanic should have done the oil. since he did the installation. he SHOULD have bottles of oil in his shop if he truly does a/c work. and has his own 30 lb. bottles of freon.

since you've replaced components. you probably don't have the lables anymore. that will say how much freon the system holds. but i'm pretty sure it's at least 5 lbs. X 16 ounces. makes 80 ounces of freon.

it should also be of note. that every time you change cans. you allow air into the hoses that connect to the system when you open and close and open the charging valve between cans.

the best way to charge a/c. is to use gauges with long hoses. have a vacuum in the system. connect yellow hose to a 30 lb. container instead of using cans. crack open top of yellow hose that connects to gauges. for a breif second to allow air to escape. and close the connection. then open blue charging handle. and let her flow into the truck. you start off with a vacuum. and charge with nothing but freon. no air in the system what so ever.

i do my own work. and always end up with 35 to 38 degrees out the vents. i can sleep in phoenix during the day with only the front panels running. no sleeper fan. the drawback. is driving a whole days shift. your chest freezes.

a properly charged and functioning system. will always freeze the dryer. instead of just simply sweating.

 

I have a 99 freighliner its ac system has 3.5 pounds of Freon. Just had the compressor replaced.

 

Not enough oil, and not enough refrigerant. Possible restriction in the condenser - either the refrigerant tubes, the fins, or both. Also remember that you have two expansion valves (or perhaps orifice tubes). You only mentioned replacing one of them. Your 'new' compressor is probably trashed now.

Get the system completely checked and flushed by a professional shop with commercial solvents. Replace any parts that they recommend be replaced, and have them charge the system with the correct amount of refrigerant. Yes, you can do the work yourself in the driveway or the truck stop parking lot. But if you want it to work correctly, leave the job to a professional.

 

With all the trouble you claim to have had the system should have been completely flushed to be sure there's no contaminants in the system. Contaminants in your lines & such is your biggest enemy for the AC.

As for me I've done most of my on AC work & never have pulled the vacuum & never had a problem with my AC's cooling or freezing up.

I once owned a 59 Ford F-100 that I completely restored that had an under dash AC. I was talking to a AC man telling him I was fixing to change the compressor them charge it with Freon. He told me you must pull the vacuum or it will never work properly

After I did this I took it to his shop & asked him to put in AC thermometer in my AC & tell me if it was blowing cold air.

It was only blowing 34º air, & it never gave me a single problem for the next 38,000 miles, that's when I sold the pickup, & the AC was still working like a brand new one.

I once bought a 1970 Duster the owner had ripped the condenser off from in front of the radiator breaking the metal lines. I cut pieces of the line off them got me some rubbers hose, connected it all back up, flushed the system to clean the lines that had been open for so long, charged it, & it worked perfectly, always blew cold air & never froze up.

 

the 99 FL i drove. was 4.25 pounds. it was a dump truck. which means no sleeper.

last time i actually worked on a semi. was a 05 w9. 5.25 pounds was the lable statement. but it was a aftermarket label.

best and fastest way to charge. is idle up to 1200. fan on. and charge till high pressure hits 140. at which point the dryer will start to freeze.

 

Never pulled a vacuum either. I do blow lines out with compressed air and install new dryer every time a line is open. I think you have a restriction or a bad thermostat switch. Something is keeping the compressor on too long and building high pressure. High pressure will start locking compressor causing a squealing belt/burnt clutch. Not familiar with freightliners but you should have two expansion valves. Low freon would not cause compressor lock up.

 

The main reason that you pull a vacuum on the system is to check for leaks. Gauge the vacuum, seal the system and let it sit for an hour or so. If the pressure in the system goes up during that time, then you've probably got a leak somewhere. Another reason for the vacuum is to evaporate and purge any moisture in the system. Moisture in the system will freeze when the system is in operation and it will clog your orifice tube / expansion valve. If you've replaced the receiver / dryer, then moisture will be less of a factor. And then there's the non-condensible air that's left in the system, which will reduce cooling efficiency. Probably not a big deal in that F-100, but more so for a big black condo sleeper idling through a traffic backup in Phoenix at 2pm in late July.

 

High pressure will also cause high temperatures at the compressor head. The high temperature will cause the oil and refrigerant to decompose, filling your system with contaminants and sludge. That sludge, contaminants and decomposed oil will cause the compressor to seize up. Definitely need to get that system flushed out.