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Recurring Problem with AC - suggestions?

touble

Seasoned Expediter
Offline
I have a 2006 Sterling MB900. This truck has had the same problem over and over again. The AC pump continues to go out. I will be replacing the 14th AC pump in 4 years. I have replaced the AC pump, AC lines, the dryer (collector), condenser, orifice, high pressure switch and have had the entire system flushed. The only thing left that has not been replaced is the evaporator. A new pump, four years ago would last about 9 months, and with each replacement or work on the AC, the life of the pump now last 2-4 weeks. Before I return to the Freightliner Dealer, there must be something, however large or small, that they are missing. Does any one have any idea as to what would cause so many AC pumps to break?

Prior to breakdown:
1. Builds high pressure in the AC system
2. Clutch does not engage
There are no contaminates in the system
There are no leaks
 

davekc

Senior Moderator
Staff member
Fleet Owner
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If the clutch doesn't engage, it is the clutch itself, or the compressor. The bigger problem is taking it to Freightliner.
History has a way of repeating itself.
Find an actual A/C technician rather than a parts changer.
Trust me when I say, there is a huge difference between the two.
 

Doggie Daddy

Veteran Expediter
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I feel your pain,our last truck ('03 IH 7400 ) was in the shop over 50 times in the 4 years we owned it just for a/c problems.

IH blamed Alumi-junk,and Alumi-junk said that they followed IH's instuctions for tapping into the a/c system.

We basically did the same as you,replacing 90% of the entire system and still no luck.

I once had a service writer at the IH shop in Canton tell me that the best that you could hope for with the 134 refridgerant was about 15 degrees less than the outside temperature. So I said to him does that mean when I am in Phoenix and it's 110 the best I could hope for was 95?

Just before we got rid of the truck I went to desparate measures,I had them change it back to as if it was a day cab,and then used a small fan to move cold air from the front to the back....it was not a good situation.

I hate to tell you this,but the cure for your problems might just be to trade it in and get something different
 

greg334

Veteran Expediter
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This will sound stupid but what does the pump do when it dies?

When you say builds high pressure, how high?

DD- what freon were they using? R-12?
 

davekc

Senior Moderator
Staff member
Fleet Owner
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Air conditioner system aren't that complicated IF the tech actually knows what they are doing. We have had several that dealers claimed they couldn't fix without replacing everything only to do a fix somewhere else for a fraction of the cost, and no reoccurring problems. To be fair, this was limited to one brand of truck. It is amazing what a few of the right fittings could accomplish.
If someone tells you that a 134R can only drop 15 degrees, that is a sign already that they don't know what they are doing.
That is a totally false statement.
 
Last edited:

greg334

Veteran Expediter
Offline
Sorry I missed that, stirring the pot and didn't read it all.

Dave, I have found out that a lot of these service people do not check the body module or the central module when they are servicing the A/C. The modules control the clutch and if it is not disengaging but hitting the hp switch that cuts the compressor clutch, it will burn up the compressor.
 

davekc

Senior Moderator
Staff member
Fleet Owner
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Just a quick side note. If replacing standard AC hoses whether generators or truck components, switch over to teflon hoses. They are much less prone to leaks.
 

davekc

Senior Moderator
Staff member
Fleet Owner
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Very smart. If running 134R in a operating unit that is running correctly, you should be at 55 to 58 degrees at the vent.
Anything else they tell you is BS.
Same standard is used for automobiles using the same refrigerant.
 

EASYTRADER

Expert Expediter
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Multiple burnt out compressors.

Tells me NO OIL in system. This is highly likely as Ive never seen a tech actually put compressor oil in. They always assume it is sitting in the condenser. It is probably NOT which is why you keep burning up compressors.

you probably need to add about 3 ounces of oil to the system. You might be able to find a can of oil at an auto parts store.

Also, if all the refrigerant leaks out, the oil leaks out with it. No refrigerant will burn up a compressor also.

However I bet they just didn't put any oil in the system, which is why it keeps burning up.
 

Doggie Daddy

Veteran Expediter
Offline
Very smart. If running 134R in a operating unit that is running correctly, you should be at 55 to 58 degrees at the vent.
Anything else they tell you is BS.
Same standard is used for automobiles using the same refrigerant.
When our last truck was working right (very rare) we could get about 48 degrees at the vent.

We can get 45 degrees in our '07 FL M2.:)
 

touble

Seasoned Expediter
Offline
A up date on the AC problem. Since I am not the best person fixing AC systems, I do believe that I have been had by a few repair shops. A Kenworth dealer in Waco Tx pin pointed the problem. The control for the heater and AC in the cab, was bad. I dont why it would run just fine for a while, then quit working, but it did. I Thank You All and stay COOL!
 
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