AC from AC?

[Andyba20]

Last week I started getting some “pre-WT” mod like symptoms. Miss, cuts, tc lock/unlock at 30-40mph especially when lugging at low rpm. Truck has wt mod, nations 180 alternator, year old batteries, new battery cables, and lug terminals. Grounds are perfect. Everything is clean. Not a hiccup since WT mod 3 years ago. Trans is a year old with 5K. 
 

Around the same time this started happening I noticed my AC wasn’t blowing cold. Charged it. Then noticed intermittent cold ac. Everything in the dash is newer (heater treater, blend door actuator, evaporator, etc)

 

Tested batteries and alternator for ac and get .01 to .015 with all accessories on or off, but did noticed a spike of up to .056 a few times when the ac compressor cycled. Could my ac clutch be going bad and causing these old symptoms to reappear? 

[Andyba20]

Guess I’ll just swap some parts and see what happens. 

[Doubletrouble]

 I wouldn't completely rule it out. I suppose it could happen.

 @Mopar1973Man might know for sure.

[Mopar1973Man]

Clutch shouldn't cycle. This is a sign your low on freon. Yup any coil like relays or A/C clutch can produce a surge or spike. If it was me I would check pressures on your A/C.

[Andyba20]

It cycles every 20 seconds or so which I thought was normal. I’ll do some testing. 

[Mopar1973Man]

No, it's not normal. When A/C is running it should lock and stay locked. Cycling will enhance clutch wear. According to Sanden Compressors it should run locked normal but no more than 5 unlocks in 60 seconds. The only time cycling is normal is DEF mode in the winter it will cycle because of ambient temperature has condensef the freon and pressures are lower.

[Doubletrouble]

2 hours ago, Mopar1973Man said:

No, it's not normal. When A/C is running it should lock and stay locked. Cycling will enhance clutch wear. According to Sanden Compressors it should run locked normal but no more than 5 unlocks in 60 seconds. The only time cycling is normal is DEF mode in the winter it will cycle because of ambient temperature has condensef the freon and pressures are lower.

 Correct. A/C on high/recirc should lock the compressor and run constant. 

[Andyba20]

So does that mean I’m within spec or no? 5 times per minute is 1 cycle every 12 seconds. Mine is cycling 3 times per minute or 1 time every 20 seconds. I’m going to get a new compressor and kit either way, but I don’t think I’ve been around another 2nd Gen that locks and never cycles. Guess they’re all showing their age.

[Tractorman]

@Andyba20, I think you are being led astray here. 

 

There are many, many things that affect compressor cycle time.  Here are a few dynamic variables that occur every day and have a major affect on compressor cycle time in a fully charged and properly functioning air conditioning system:

 

*  blower fan speed

*  recirc or outside air

*  ambient temperature

*  ambient dewpoint

*  engine rpm

*  air flow across the condenser

*  sun load

 

So, without naming some parameters, no one can say what is normal for compressor cycling frequency.

 

On our 2nd generation trucks, compressor cycling is controlled by a low pressure switch downstream of the evaporator core.  When refrigerant pressure falls to around 30 psi, the compressor will cycle off.  30 psi equates to about 30°F.  This means that condensation from air passing through the evaporator core can collect and freeze onto the core which would impede air flow into the cabin if the refrigerant pressure remains at 30 psi or lower for a long period of time.

 

When the cooling demand is low (75°F ambient air, 45° dewpoint, blower fan on low bringing in outside air, truck parked in the shade), the compressor will cycle frequently - I am not going say how frequently.  When the cooling demand is high (85° ambient air, 70° dewpoint, blower fan on medium bringing in outside air, truck parked in the sun), the compressor will probably run continuously.  It isn't "locked on", it simply cannot reach a low enough suction pressure to cycle off.

 

Now, with all of that said, if your truck's cooling demand was high and it was hot outside and your compressor is cycling frequently, then it is likely there is a low charge of refrigerant in the system.  Recovering the refrigerant and weighing what goes back in is the most accurate method for charging the AC system.

 

- John

 

 

 

[Andyba20]

Good info @Tractorman, hopefully I’ll get the new hardware installed while we still have a few hot days left here so I can compare before and after cycling. Kinda hoping my compressor clutch is bad so I don’t have to spend a bunch of time and effort chasing down whatever is causing the issues I’m having. 

[Mopar1973Man]

Only a small tweak it is 25 PSI for most Mopar Products.