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View Full Version : Losing AC on a long uphill grade?



Clod Hopper
September 8th, 2010, 09:25 PM
99 Superduty, crew cab long box, 7.3 with minor kick on power. I have noticed on long uphill grades while towing (8k total) the AC quits. Blower still on but cab gets warm and as soon as cresting the hill and the boost drops back down, the air gets cold again quickly.

At first I thought it might be an overheating issue. But my coolant gauge never even budges. Maybe the sender is bad and isn't telling me the right story.

So, is the loss of AC on long high boost pulls normal? Or do I need to dig into it more? I can see it might be designed to do this so as not to further load the coolant system.

Big Dave
September 8th, 2010, 10:02 PM
I usually don't have the a/c on when I'm on a long hard climb like Eisenhower or Vail, I guess I'm too impatient and want every ounce of power available. But I'm not sure how much I trust the factory water temp gauge, I've always thought of it as more of an idiot light. It's max temp has never really changed, even towing in 105+ heat with the a/c blasted.

Cresso
September 8th, 2010, 10:43 PM
I know several vehicles are designed to disengage the A/C clutch when throttle gets to a certain percentage. Maybe not all, but I betcha most do it. I'd wager that's what you're experiencing.

Phazertwo A.K.A Brenden
September 9th, 2010, 07:15 AM
i know several vehicles are designed to disengage the a/c clutch when throttle gets to a certain percentage. Maybe not all, but i betcha most do it. I'd wager that's what you're experiencing.

x2

pz

scottycards
September 9th, 2010, 07:41 AM
I know several vehicles are designed to disengage the A/C clutch when throttle gets to a certain percentage. Maybe not all, but I betcha most do it. I'd wager that's what you're experiencing.

Correct. Vacuum-actuated AC clutch. When under high load, AC cuts out.

CSP
September 9th, 2010, 08:11 AM
No vacuum on a diesel engine. ;)

Could be another method, but there's no vacuum switches on it.

co84rc
September 9th, 2010, 08:45 AM
its part of the ECU/ECM strategy on most computer controlled vehicles.

scottycards
September 9th, 2010, 08:58 AM
No vacuum on a diesel engine. ;)

Could be another method, but there's no vacuum switches on it.

Ok, tps sensor activated...........:flipoff2:

Clod Hopper
September 9th, 2010, 01:14 PM
its part of the ECU/ECM strategy on most computer controlled vehicles.

This is what I was thinking. It comes back to cold too quickly at the top of the hill for it to be overheating. But, it doesn't hurt to tap the vast knowledge of the worlds top minds. Oh and you guys too. :flipoff2:

MDert
September 10th, 2010, 07:34 AM
My 99 does the same, I havent looked into it, just accepted it because I dont think it should be used accelerating on hills or passes anyways. Ive seen it on other superduties too FWIW