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Big truck AC specs?

chris142 on Wed August 01, 2007 9:56 PM User is offline

Country of Origin: United States

I made the mistake of repairing a guys KenWorth. Since then all his friends have been coming to me. Seems that every truck is different. Especially PeterBilts. Some have Orifice tubes, others have an expansion block, big condensors and small.

Where can I get refrigerant capacities for them? Most don't have a sticker. Peterbilt dealer is no help.

bohica2xo on Thu August 02, 2007 2:58 AM User is offline

Generally, all you need is a blindfold, a dartboard, and a ouija board...

Class 8 trucks are assembled to customer's specs by gorillas high on crank, directed by chimps on crack. I believe the build orders are processed by a blind, 100 year old pakastani woman who knows only 3 words in english...

(Now if I have offended anyone that keeps primates as pets, or has an aging pakastani grandmother, I am truly sorry.)


Low (compared to car lines) volume, with considerable differences between each vehicle on the line, coupled with low bidder supply practices mean you will rarely see two trucks alike. I can name a couple of places that put bodies on Class 8 trucks, where you would be amazed anything worked when it left the facility.

I had to help a company defend itself after they got sued for substandard performance on a product. Their product was an oil flooded screw compressor for firefighting equipment. The truck assemblers insisted on using a kit for a different engine (cheaper) and fabbed their own brackets. The compressor was supplied with a poly-vee electric clutch, and a mating crankshaft pulley for the CAT engine it was meant for. They swapped the clutch out for a single vee belt unit, and chose an existing engine pulley. The OEM drive was 6:1 overdrive for the compressor. The finished product as delivered to the firehouse was 1.5:1 overdrive. The mechanic said in open court " that looked way too fast anyway. It'll last a lot longer slowed down". I saw pages of faxes warning them about underspeeding the compressor.


Back to your question.
Treat every system as if it is a custom install - because that is basically what it is. They are coming to you because you took the time to make the first one RIGHT. Just charge them accordingly. Keep an eye out for underdriven compressors too!

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Thu August 02, 2007 6:58 AM User is offline

Refrigerant shouldn't be a problem, pressures will get you through that. Somewhere way back, Detroit_AC in a discussion with Mitch explained the procedure for determining the amount of oil a system requires. As I recall, these were on the two cycle engine type systems where you are working on a refrigerant oil mix of a particular ratio to assure proper lubrication. After all, only the compressor requires the oil, it's in the way for the rest of the system. It was a rather involved cut and try procedure, not really handy for shop type work.

Seems like in motorhomes, they prefer some type of a compressor using a sump, they claim the oil used must be compatible with the refrigerant, and all you got to do, is to make sure the sump is full, the most typical compressor is the York, but Tim recommended using a Seltec, but I never learned if this compressor has a sump or not, if not, back to the two cycle engine type compressors. Seems like most ratios of refrigerant to oil are in the 3 to 5 parts of refrigerant to oil, by weight range as a ball park figure.

Not that I am recommending this, could start off with a 5:1 ratio and try injecting more oil if the compressor is noisy until it quiets down a bit. Or just insist on using a compressor with a sump in it. In my opinion, sumps should have remained. I go nuts in trying to figure out the ratios of gas to oil in two cycle engines, but tend to go on the rich side to prevent engine failure. But then, have carbon built up problems, can't win.

chris142 on Thu August 02, 2007 9:44 PM User is offline

I never thought of an underdriven compressor. Some retrofits give me fits and I just cant make them work right. Thats a definate possibility.

So far the Petes that are day cabs and have the small condensor work ok with 1.8lbs of r134a. Larger condensor likes 3.0 lbs r134a. The expansion blocks seem to be more forgiving than the ones with the orifice tube.

The sleeper trucks give me fits! I just can't get them to work.

NickD......I prefer Torco GP-7 @ 40:1 unless I'm dune riding then I go to 32:1. I ran a 1982 ATC 250R for 15 years, riding 100+ miles a weekend like this for 15 yrs and never even pulled the head.

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