AC not quite as cold

[Mopar1973Man]

No. Just bring the RPM's up and see what your pressure are like. See if the compressor is going to excessive cycle out. Remember you DRIVE your truck not IDLE in parking lots. So the A/C should be charged enough to prevent excessive cycling. Now under normal operation eventually it will cool the cab to the point you turning down the fan speed. Now I except the compressor to cycle because the evaporator temperature will fall even more. So the lo side pressures typically fall more. Then mild cycling of the compressor will occur because of excessive cold temperaure and prevent freezing of the evaporator.

 

To see this happen roll up the windows let the cab cool on MAX A/C and now turn the fan speed to low and watch the lo side pressure it will fall to about 25 PSI and kick out the compressor. Look at the inner ring you'll see the discharge temperature is just below freezing. Optimally you want enough freon to keep the evaporator sweating. Hence why I normally head towards 35-40 PSI so when the vehicle is driven the lo side as close as possible to the freeze point without trip the lo side cutout.

 

[leathermaneod]

Ok that makes more sense now. Unfortunately I don't have the equipment to see all that. I guess what I'm asking is, why was I not able to charge above 25 psi? And if I set high idle and the compressor unlocks too much Would I be able to add more freon with the rpms up?

Edited August 5, 2016 by leathermaneod

[Mopar1973Man]

Because as you discharging the can into the system the can got cold. So what I typically do is fill a small bucket or pail up with hot water and place the cans in hot water to regenerate pressure. Basically you need to keep the freon above the boiling point.

[leathermaneod]

Ah now I understand. It would be nice if the instructions had told me that lol I'll try at higher rpms and a warm can when I get home and see if I can get it charged up a little more 

[IBMobile]

134A boils (changing state from a liquid to a gas) at -15.34°F.  When the 134A is discharging from the can both the volume and pressure drops in the can when that happens the temperature drops also.  Bring the heat up and the pressure comes up.  I believe this is the equation for it  P₁V₁/T₁=P₂V₂/T₂.

[leathermaneod]

Thanks a lot guys! Mike, I followed your advice with the warm water and heating the can up in between charging. Got about 35 psi now but that was at 89° so it should be more like 50 psi per the fsm, but I've already added about 32ozs of refrigerant. I did get it to where the compressor stays locked at 1500rpms now, but on my way home I had max AC on for a while before it got cool enough to turn it down. I'm wondering if it's still not enough psi to keep the comp locked at 2000 rpms which is where I spent most of my 5hr drive.... don't get me wrong it was cold, just not that cold. I'm going to check tomorrow and see if the comp stays locked at 2000 rpms. If not should I add more refrigerant?

[Mopar1973Man]

I would stop there. Like the foot states if the pressures are below and discharge temperatures ar good then your fine.

[leathermaneod]

What if the compressor isn't staying locked at higher rpms above 1500 though? 

[Mopar1973Man]

Here is where I need to see the high side pressure. I need to be able to look at lo and hi side and then I can base the amount more so. 

[leathermaneod]

Well I'm at my inlaws right now and my father in law has a gauge manifold so maybe I'll hook it up tomorrow and see what it looks like. What do I need to know/look for when doing that?

[leathermaneod]

Well here are the results from testing with the manifold gauge. 

What do you think? Add more freon or no? Compressor stayed locked at all speeds. Outside temp is 86° and very humid. Air at the vents is pretty cool, just not ice cold yet. Even at highway speeds I don't feel like I can take it off max AC for a good while.

 

Idle:
Comp locked:
High-230psi
Low-39psi
Comp unlocked:
High-
Low-

 

1500rpm:
Comp locked:
High-283psi
Low-30psi
Comp unlocked:
High-
Low-

 

2000rpm:
Comp locked:
High-285psi
Low-27psi
Comp unlocked:
High-
Low-

Edited August 6, 2016 by leathermaneod

[Mopar1973Man]

You pressure numbers are fine just the hi side showing that the condenser is running a bit hot and not discharging heat very well. Fan clutch might be weak or the condenser is plugged up with bugs.

[IBMobile]

Test the center air duct temp with the A/C off first to see if it is the same as out side air and be sure the blend door is closed all the way.  Then run the A/C through the enter vent on max A/C (this stops out side air and is in recirculation mode) turn fan on to #3 bring rpm up to 1500 and if you can put a fan in front of the radiator and turn on med to high speed.  the fan in front of the radiator and 1500rpm simulates driving at about 35mph and you should see a duct temp below 35°

[Mopar1973Man]

Thanks @IBMobile... That good info... 

[leathermaneod]

Thanks guys for all the great info! You've been very helpful and I've learned a ton about AC! I've got to drive home tomorrow so I'll see how it does. If it's still not cool enough, I'll test the actual vent temp as you suggest when I get home.

Edited August 8, 2016 by leathermaneod

[Mopar1973Man]

As for testing vent temp buy a cheap digit kitchen thermometer and use it for testing the vent temperature. I've seen weird reports from IR temp guns and different color changes the temperature displayed. 

[dripley]

My thanks to @IBMobile and @Mopar1973Man for all the useful info too. It has helped getting mine going again.

[Mopar1973Man]

Just thinking about this @IBMobile might be a good idea of teaming up building a new A/C article built around both of our ideas. It would be awesome. 

[IBMobile]

A thought similar to that ran through my head this morning   I'll pm you later.

[Mopar1973Man]

Or... Just give me a shout at (208) 628-3645 we can talk about it.

Edited August 7, 2016 by Mopar1973Man