Case air cond. guru,s???

I'll try to keep this short. '74 1070 , put new bearing/seal in compressor (York). Charged air last nite. Used jumper wire to comp to fascilitate faster charge. Everything worked great. At 1500 rpm and full air just about froze cab. This morning , buttoning things up. Hooked factory wire back to comp. Would not cycle or kick in clutch. Hot wired to make sure charge didn't leak out over night and it blew very cold again. Still charged. Checked voltage at wire,11.52. Set meter on frt tire and from inside cab, turned switch on/off several times. Meter "0" when off and 11.50 +/- when on. Takes 12.5 to energize apparently 11.5 won't do it. Set meter on amp draw between batt voltage and wire to comp. Naturally clutch energized and meter read 3.95-4.00. One spec in serv man says 4.44 another page says 2.7 - 3.3. Maybe different brand comp or updated spec who knows. My 3.95 seems to fall right in the norm either way. Bottom line is , both hi and low pres sensors are working because I,m getting same voltage whether I by pass them or go through them. won't do anything. What am I missing here? Are they that sensitive and if they are then thousands of them have likely to have been replaced? Every bulb, electric item on this tractor works perfect and so does the air when it has 12.5 volts. SOOOO close but no cigar. Somebody's had this problem sometime. They are all made the same. Any help welcomed. RB

My 970 would work good for 2 hours and then quir cycleing. The compressor would cycle off and then not come on again. If I would turn the fan off and back on that would raise the voltage to the clutch just enough to get it going. When I had enough of that I mounted a relay to get more power to the clutch and have not had an issue since.

Is it possible that the 4 position speed control switch or the temp control that it feeds or the both of them are responsible for "eating up " that one volt of needed power? I know there is full (12,5 or so) comming up to those controls ans have suspected them but just can't bring myself to believe that clutch magnet is THAT fussy. Thanks for your post and I'm sure there are more that had this problem but it's late , will probably hear from them tommorrow.

Every connection, and every foot of wire results in voltage drop. My guess is that heavier wire would do you more good than a different switch. My experience with switches is that when they go bad they go really bad, and voltage drops more than what you have. The guy that services my AC told me that it is a common problem on older machines, and he installs relays on all of them after seeing how the relay worked on mine.

(quoted from post at 07:55:41 05/18/13) My experience with switches is that when they go bad they go really bad,

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This. 970s light switch caused me similar issues last fall. Phantom voltage drops, constantly blowing the circuit breaker, lights only getting 8V, even though the meter said 13 with them unplugged...

Face it, these girls aren't supposed to still be in service.

AP Air offers a relay kit P.N. 220-405, which is installed on most all AC,s I work on, or someone like NAPA cold fix you up. Other option would be to trace wire and check all connectors. As R.G.M. stated, your tractor got some age.

Had the same trouble. after the dealer replaced everything two times and I still had trouble. I just unpluged the AC pump from the auto controls and just wired a switch which I turn on and off to get my right amount of cooling. This bypassed high pressure switch and low pressure switch. All AC experts says I"ll ruin my compresser. One compresser was ruined but it had a rod break witch had nothing to do with my way of doing things. That compresser lasted two days and the dealer replaced it.

By the way! I did this 20 years ago and have had no trouble. Works great. The big drawback is I become the thermostat.

Thanks for all your input guys. I believe I will mount a relay up by the hi/lo shut-offs in front of radiator/condenser and use the wire from cab control (11.5 V) after it goes through the hi/lo safety switches to control the relay which I will wire to the bat term on back of alternator and output to compressor clutch. Cab still controls everything and will still have hi/lo protection. Thanks again. I knew someone had allready had this problem somewhere. RB

A relay feeding the clutch is always a good alternative to overcome ageing wires and connections. Doesn't take much of a connection to operate the relay and you can wire relay into a good power source with good wires.

Just a thought, maybe the air gap in the clutch is too wide,they do wear some after years of use, takes a little more juice to suck it shut. The relay sounds like the way to go.