Ask the Mechanic

AC Clutch Burns

READER: I am having trouble keeping air-conditioner clutches in my 7800 John Deere tractor. I had the John Deere guy come out, and he told me that my pressures were good in my air-conditioning system. My neighbor had told me that I probably had too high head pressure. I guess that is not the case. The system does not freeze up and cools OK for a few hours, then it begins to get hot in the cab, and the clutch on the compressor slips and burns out prematurely. I have had some starting problems in the past, but as long as I charge the batteries overnight, it starts and runs fine most of the day. Could my batteries be getting low and need to be replaced? Could my alternator not be charging and causing starting and air-conditioning problems?

STEVE: I believe you have found your problem, and the problem is with the amount of charge in your batteries. The batteries must stay up to handle the electrical load on your tractor. As your batteries begin to lose voltage to the point where they won't supply enough amps to keep your compressor clutch hooked up, the clutch will slip. The clutch is a magnet that is activated by adequate amps from your battery. With the engine on the tractor running, check to see what voltage is in your battery. It should be one to one and a half volts higher than the voltage checked with the tractor not running -- which should be around 12.6 to 12.7 volts not running.

READER: I am having a lot of problems with customers complaining about dirt being in the hay that I sell. Can you give me some tips on how I can help eliminate that problem? I am currently using a wheel rake, and I would like your advice on which rake you recommend from a mechanic's point of view, keeping in mind maintenance costs of the different types of rakes.

STEVE: It seems these days that hay customers are really concerned about the amount of ash, which is the total mineral content after burning a sample, is in their hay. The University of Minnesota has done extensive tests on the amount of ash in hay when raked by different types of rakes, and studies show the wheel rake leaves the most ash of all the types of rakes. I guess that makes sense because the wheel rake's teeth use the ground to drive the rake, and the bar rake's teeth run above the ground (unless the hay ground is rough, like mine). However, the wheel rake costs less than a mechanically driven rake to purchase and, because it needs no drive shafts or gearboxes, normally costs less to maintain. I have used both types of rakes and have found that when raking hay following plowed stubble, the bar rake will windrow hay with less ash.


I know this tip is a little crazy, but accidents often happen because of something unexpected. However, what happened to me was a surprise provided by a round bale of hay. Yes, a round bale of hay. Rolling on me? No. Falling on me? No. Unwrapping on me, yes. We had stacked some string-tied round bales too close to the corral last summer, and the cows reached through the pipe and ate about a third of the hay off the side of the bale. The bale was held together by string, but the bale was way out of balance. I forked the bale, went to the pasture and cut the string with the bale held up slightly in the air by the loader fork. I stood on the "heavy" side of the bale and began cutting the string. Suddenly the bale unfolded with much force on me. If I had not been standing near the end of the bale, I could have been injured. Lesson: New lessoned learned!

> Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email


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