[jleedog]

I have a problem with my A/C (or Defroster) cycling on and off while towing my fifth wheel when going up grades. The system will work great when im not towing or on level ground. I took the truck to a A/C specialist that could not find anything wrong with the system. He even added a little bit of Freon to see if that would help. It didn't. He had hooked up his AE to the truck and said that all the numbers were right were they needed to be , but I cannot replicate the problem unless Im towing so he could not see a problem. The only way he said was to bring the truck and trailer in and we would have to go for a ride with his AE hooked up to see if there was something wrong. The compressor will cycle on and off every 2-3 seconds when its happening. Do I need a new compressor? Hooking up and driving the tech around seems like a lot of hassle and possibly $ that I would like to avoid. Any help is appreciated. Thanks Guys

 

[RT]

Honestly, I don't know if this is a feature built into our trucks but a lot of vehicles will kill the a/c above a certain throttle position just to free up power. Short cycling is usually caused by the low pressure switch, but there is a high pressure switch as well and the pressures would be higher towing uphill as the condenser is going to be exposed to a greater heat load from the radiator. Are you downshifting on these uphill runs?


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[jleedog]

RT I drive by my gauges so when I need to I drop into a lower gear, but I am never in overdrive. Would AE be able to tell if the low pressure switch is coming on/off? I haven't always had this problem so I don't think its a safety feature.

 

[jleedog]

Is it possible that changing the air gap on the compressor clutch could have caused this?

 

[RT]

AE won't see the pressure switch. Nothing in our model is monitored by the PCM. The air gap shouldn't have caused this. I would run a LED light from the a/c harness into the cab. Start at the compressor. If you have power, but the clutch is dropping out, you know it's clutch related. If the power is dropping out, move the led to before the low pressure switch. If the power is constant there, you know your pressures are dropping. Since adding refrigerant didn't help, it could be a restriction in the system showing up at higher RPM. Think orifice tube.


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[jleedog]

So just hook up 2 wires to a (test Light) one to power one to ground and see what happens on the cluch and pressure switch right?

 

[RT]

Exactly


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[jleedog]

Where abouts should I hook up the light before the low pressure switch. A pic would be nice.

 

[RT]

There are two wires on the low pressure switch. One is hot going into the switch, the other is the output that leads to the a/c compressor. Do you have an ohmmeter?


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[jleedog]

Yes I have a meter what side should I tap into

 

[Maryland dieselnick]

Is it possible that changing the air gap on the compressor clutch could have caused this?

You changed the air gap??

 

[RT]

Yes I have a meter what side should I tap into

OK - first, we need to find which side of the low pressure switch is the hot side and which is the output side. You could do this one of two ways. Using your voltmeter, unplug the harness and with the engine running, a/c on, check for voltage on the two pins of the harness. Alternatively, you could set your meter to ohms, put one side on the compressor harness (the positive lead, not the ground lead) and then probe the low pressure switch harness to find which wire connects to the compressor.

On the LED hookup, I would ground one side to any convenient ground and then put the positive lead in with the positive lead of the compressor first. Then you can see what the compressor is being commanded to do versus what it is doing. If it is getting voltage, but not engaging - you've got a clutch issue. If the voltage is cutting out, then move the LED positive lead to the input lead to the low pressure switch. If the current is constant there, you can assume it is the switch cutting the a/c off (indicating a refrigerant issue / restriction). If the voltage TO the low pressure switch is cutting in and out, then you have to go further back to the switch / a/c relay / some other aspect of the system.

 

[jleedog]

Ok RT, I have hooked up the lights as you say. I had both of them react the same way. When I have the AC running they are both on. When I start going up grade they will both cut out and come on.

 

[jleedog]

Took the truck to an AC guy today, he pulled out the orifice tube and it was clean. He thinks the problem is the truck is killing the power to the AC to keep up with demand and that is why it is cycling on and off.

 

[jleedog]

It may be that my tuner has caused this problem. I don't remember having it before I had installed it? Anyone else had this problem?

 

[RT]

I have never experienced this but I don't tow hills. Call Justin or Jody and ask if this is part of the program. While I understand the concept of dropping the compressor under load when you're driving a 4 banger and the a/c is 25% of the load, on our trucks it just shouldn't make any difference.


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[jleedog]

I have spoke with Justin. He says that there is no comm between the ECM and the AC. He wants me to put the tuner into a higher HP mode to see if the problem goes away with an increase in horsepower. I will try this on my next trip to see if it works. Might be a few weeks before that happens. If it stops the problem I might install a WW2 to increase the HP a bit, because I would like to keep the shift points of my 60 hp tow tune.

 

[jleedog]

Well I took the trailer out for a trip this past weekend and did some testing to see if I could isolated the problem. Set my tuner to the max (80hp) setting and the problem did not go away. Set my tuner to stock position and the problem did not go away. This is starting to upset me that I cannot find the problem. I hate to start throwing parts at it, but I need to resolve this issue. Do you think a new high and low pressure switch would help? Lack of power to the engine and the computer shutting the AC off does not seem to be the issue(but I could be wrong)Faulty compressor? I cleaned the evaporator and the radiator is clean. The system works great unless I am towing under load going up steep grades. It seems that plenty of others would have had this problem if it was a computer issue. Any suggestions? I am running out of options.

 

[jleedog]

Well I talked with a guy with the same truck as mine that tows heavier than mine and he does not have the same problem. Another friend of mine that tows heavy has the same problem I have. So I am getting confused again. Took it tan A/C guy and had him add 6oz more Freon the system(as suggested by a Ford tech) and had him replace the low pressure switch. Test drove and had the same issue as before. Starting to get super frustrated.

 

[79jasper]

Did you finish the tests rt said?
As said above, the pcm can't shut a.c. off.

And you never answered post #11 asking if you messed with the air gap.

In my wee mind of a.c. you may have a clutch problem. It's a electromagnetic clutch. Resistance will weaken the "pull." Heat creates more resistance. (Towing heavy = more heat)
So... I would say too much gap or weak clutch.

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