j_martin

That would be a likely answer. 450 lbs is about 210 - 220 degrees condenser temp.
Another common problem is shrouding / air flow path.

ofelas

Just realized it doesn't cycle off only when in Drive.
Park/Neutral results in normal cycling.
Im idling at 850rpm Park AC off
Idling at 650ropm Drive AC on.
Shroud is good. Fan blades are good.
Paper against the rad gets stuck on the rad surface.
Paper against the condenser doesn't.
Condenser is clean with 95% straight fins and all surfaces degreased.

j_martin

Air flow. If the condenser is too far in front of the rest of the assembly, air is pulled in from the side, bypassing the condenser.

Or plugged condenser fins.

Refrigerant side, the system is functioning well in all aspects.

ofelas

Fins are straight, some plugged by bug carcasses/tiny gravel. Tip of a steak knife got most debris out but I reckon i will air hose it using an L-fitting from the rad side to blow the remaining debris out the front of the condenser.

Condenser & rad are in the stock locations.

Were there factory rubber flaps sealing the sides of the condenser to the rad tanks & if so, could you upload a pic?

Could you also check to see if your condenser front surface hold a piece of paper at idle ?

My drive AC idle at 650rpm too low ?

j_martin

Don't worry about the fact that it's not cycling at idle. That is normal. It just means that the system is falling off 100% at the slowest speed, which is a compromise to keep from wasting too much HP (and fuel) at normal speeds.

Is the rubber flap across the top of your radiator frame sealing the radiator to it missing?

ofelas

Understood; though the always on/not cycling/450psi high side pressures until the compressor turns off worries me.
No rubber flap....danggit.

j_martin

There it is. Air is bypassing the condenser. It won't take the heat (pressure)off the freon without air flow.

Some times the simplest things bite you right in the afterburner.

maybe368

In case you haven't already done it, have you tried another set of gauges? As was said above, maybe you have a faulty high pressure gauge...Mark

j_martin

Naw, it makes sense. With poor airflow to the condenser, it'll climb over 200 degrees pretty quick. the temp/pressure curve isn't linear. At 200 degrees, it'll gain 4-5 lbs pressure per degree. That rubber flapper dohickey is critical with AC. It's pretty important with an intercooler also.

ofelas

Yes. Gauges good, checked against another vehicle.
Made my very own rubber sheet flapper doohickey - no discernible difference, pressures still high, though only 400 or so now.
HD factory second gen fan clutch next...will be here on Wed.

ofelas

The only thing i can think of is fan clutch not pulling enough air through condenser at idle...as the airflow is fine above 1000 rpm & brings the high side pressures down from 400psi to 220-240 psi pretty quick.

Or, the half empty R12 tank had air in it...but still wouldn't explain why it works above 1000 rpm.

Weird.

maybe368

Well, I think that there is an easy way to test that, put a big fan or seveal smaller fans in front of the condenser and see if the pressure drops at idle. If so, you have your answer...Mark

ofelas

Got mine finally fixed.

My **** fish scales were bad; there was a low charge in the system.

Vacuumed the R12 out, refilled 38oz R12 on a digital stand scale.

Vents are blowing 36F air with ambient of 87F and 88% humidity.

Pressures are 36psi low and 195 high.

Compressor cycles 4 times a minute for 10-12 seconds a time.

New clutch went in anyway...holds a dollar bill against the front grill even while the fan is freewheeling at idle. Old clutch didn't do that.