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funny fan
Replaced fan clutch during down time this spring and several trips since with no problems. N ow on weekend trip and during check in at campground with coach on high idle and with dash AC on noticed fan cycling on and off at about 15 second intervals. Stopped doing that when dash AC turned off. Replaced 79 relay with spare I had with and no change. Broke tab 85 off and fan runs on high all the time. With dash AC off turned off and normal relay in place, fan just free wheels as expected at idle. Of course, don’t know at this point how clutch will function going down the road. So options are to just leave dash AC off and normal relay in place and see what happens with regard to expected cycling while traveling or leave relay with 85 tab broken off in place at location 79 and let fan run on high for trip home. In any event, can’t figure what is going on. Bad signal from the dash AC???? Relay 99 bad????? How to investigate??? Need input to my feeble mind. Thanks. Mike
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8 Replies
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My guess is your dash ac is cycling on and off for whatever reason and so the fan clutch is following suit, something that’s necessary when the ac condenser is mounted on the radiator.
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Don:
Is that something I should be able to notice in the performance of the dash air? Seems to work ok grossly. ? how to check. Mike
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I think that Don is probably right on target. I believe that the fan comes on when the dash air is on regardless of the coolant temp.
JC
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
I am with you on that. Turn dash air on and fan runs in high mode continuously normally. Any thoughts on how to investigate this problem? Does that fan signal from the dash AC go through the DDEC and then to relay 79???? Mike
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Causes of ac short cycling which causes both the ac clutch and fan clutch to engage and disengage in brief intervals:
1) being slightly low on freon
2) faulty ac pressure switch
On buses with Prevost full OTR system, the condenser is located mid-bus and has large 24v fans to draw air thru it, so the Detroit engine fan clutch is not linked to ac operation.1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
Great help from Don over the phone. Thanks so much. Agree most likely AC compressor clutch short cycling. Would seem easy enough to just replace that pressure switch that signals the compressor clutch. Now where to find it. Anybody know where that would be located? Interestingly, when I started the bus today and turned on dash AC, things worked like they were supposed to. Love intermittent problems!!!
Going to replace that pressure switch if I can find it. Mike
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An intermittent issue is often related to a loose connection or bad ground. That might be a good place to start.
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Jon:
Looked for all that. No find. All works great when I break off tab 85 on the high speed relay (79) and I’m thinking that if wiring problem, then would still have problems. With tab 85 broken off, takes the feed from the pressure switch out of the equation – I think. Mike
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