AC clutch won't disengage

chumwon

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Howdy everyone, my 1990 dually finally wouldn't blow cold air anymore and the clutch would go on and off every 5 seconds. So I did the right thing (not) and decided to get a can an throw a little freon in her. Well, after putting maybe a half a can in the ac started to blow pretty cold again but the ac clutch will not cycle. If I turn the air off it un locks but once I turn the ac back on she's permanently engaged. It actually even made my truck start to heat up while sitting. It has been converted to 134a by original owner. I even tried to bleed some out the low side to see if that'd help but it doesn't seem to.

Any ideas or direction to look at would be greatly appreciated. I'm just not very knowledgeable of how the ac system works.

Thanks everyone!
 

Nero

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You need to hook gauges up to it to see what the low and high side are doing. It running constantly isn't necessarily saying something is wrong. There's a pressure switch on the side of the accumulator, once the low pressure gets to a certain point, it'll turn the compressor off, it may not be meeting the threshold.
 

Rdnck84_03

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On a correctly functioning a/c the compressor should never shut off when turned on. If it cycles on and off is usually a sign of low freon level.

James
 

Booyah45828

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What those guys said.

The proper way is to measure in(weight) or out the correct amount of refrigerant. The improper way, that can work, is to add refrigerant based off the gauge readings(both sides, not just the low). The wrong way is what you did, and that is adding refrigerant without knowing what's actually happening in the system.

The underhood heating up is also normal, as that's where the heat that was in the cab goes(condenser). If your fan clutch isn't up to snufffff, running the ac can also lead to higher engine temps, but you'll likely blow the pressure relief valve on the compressor before that happens to an IDI.

Edit: Apparently s-n-u-f-f is a bad word now.
 

chumwon

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Yeah I think it might be time I get some gauges. I was just being lazy and hoping a bit would do it. My clutch fan doesn't really work either. I noticed it in the past but has never dreamed of getting hot. I guess that might be what's up next to address on the ole girl. Thank you very much to each of you for your advice!!
 

Nero

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I have a factory brand new fan clutch ive been trying to move for a minute if you're interested
 

gnathv

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Is your low pressure line (the big one) condensating (getting wet) from your evaporator (black box on firewall) to the back of your compressor? Is there a steady drip out of evaporator to ground by front passenger tire? What’s air temperature coming out of your vents in the truck?
 

franklin2

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Cycling the clutch with the low pressure switch is how Ford controlled the cooling of the system. And it monitors the overall pressure in the system. So it had two duties.
1. How cold the evaporator is (the coil in the dash) is directly related to the pressure at the pressure switch. Colder means lower pressure, hotter is higher pressure.

2. Low refrigerant levels means the whole system pressure will be low. This kills the whole thing if there is not enough refrigerant in the system.


Whether the compressor cycles or not is directly related to the ambient temperature of the evaporator coil in the dash. If you have a lot of warm air blowing over the evaporator, then the evaporator stays warm, the pressure will be high, the compressor will not cycle. On a cooler day, if cool air is blowing over the evaporator, then the evaporator will be cooler, and it may cycle some.
 
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