Ac blows cool on Max ac :(

[Pwrcummins]

It's summer in Texas and driving a black truck with black interior. Time to start using the ac especially when I get done workin out at the gym. Ac is a must! It's been blowing cool for awhile and at night it's a little cooler than during the hot day. So I proceed to the auto parts store and get some ac refill with a gauge. I head home and plug the ac recharger with gauge on the low side with ac on max. It reads deep into the red and ac compressor is spinning. So I'm thinking ac system is way over charged and with that being said the ac compressor stays on due to the high charge. Could I be wrong? Am I doing something wrong? Not very experienced in the ac part of vehicles/diesels.

 

[Atsah]

Don't know about the gauge on those canisters you can buy but, if you put the ac on max (which recirculates inside air) and leave the fan low, does the compressor cycle?

 

[Pwrcummins]

I have not tried on low fan setting. Should I also put it on regular ac instead of Max ac?

 

[Atsah]

I have not tried on low fan setting. Should I also put it on regular ac instead of Max ac?

Max uses less fuel and the compressor doesn't have to work as hard because the air in the cab is cooler than the outside air..

 

[Pwrcummins]

Did not know that. I figured max ac would be freezing your butt off lol

 

[Fordguy100]

You need a set of gauges, so you know the low side, and also the high side pressures.

Go rent a set from autozone and take a look. My bet is the compressor is going out. When they start to go bad, the compressor cant get the low side pressures down low enough, so they wont cycle on and off.

Does it get noticably warmer when you come to a stop?

http://www.youtube.com/watch?v=i9yv0euT7xA

 

[Pwrcummins]

No onece it's cool it's fine just takes a little bit to cool down

 

[Pwrcummins]

So I turn the truck on and try it on low fan setting and just at ac not max ac. The compressor is still on but won't cycle on and off. Now if I turn it to the next setting on the far right knob to the sitting man with arrow in face bye compressor turns of and no ac. I also tried heat on for kicks and giggles and it got warm but not like sauna. Which I guess is good. The ac never really got any cooler on just regular ac vs max ac. So I want/hope the ac compressor is still good and it's just a really over charged system.

 

[Tx_Powerstroke]

I would buy a set rather than rent a set. There is no telling what the previous renter did with them if the lines were cleaned properly, any contamination inside the lines. Thats why when I got epa certified epa 608,609, and universal I bought my own gauges to know where they have been and what they were used on. I;ll have to find the formula for what your gauge readings should be but it all depends on ambient temp.

And when its running are you seeing any frost on one side of the compressor lines and almost none right after it?

 

[Pwrcummins]

Tx Powerstroke glad you asked about frost. i did look and the lines are cold but not frosty or have any kind of condensation. So at the moment the info that i have is low side is high and cold but not frosty ac lines with ac compressor on unless turned off inside cab. i think its sinking in that the compressor may be going out, and that does not look like an easy job. lol.

 

[Pwrcummins]

could the pressure switch be bad? im going monday to a friend of mine to have the system checked to see what psi the high and low side are at. im also afraid that the compressor is good and what ever the problem is could harm the compressor

 

[Tx_Powerstroke]

well if it was frosty then nothing right after it could be a sign of a bad orfice tube or restriction in the system. I'd have them check your psi's and go from there could be low on r134 also.

 

[Lethalthreat7.3]

Tasha is correct in saying it is cooler on max AC because of the cab air. Max is recirculating the cab air through the evaporator coil where the regular low thur high pulls outside air across the evap coil.
The compressor cycles on and off depending on interior cooling load and air flow across the coil cycling off on the low pressure switch. As the interior temperature cools and the air drawn over the evap coil continues to drop in temperature the low pressure side of the refrigerant system also drops.
So if you start the truck and the interior is 110* the low pressure side would be running in the 50psig/"Red" range because of the high air temp being drawn across the evap and the refrigerant absorbing the interior heat which raises suction/low side pressure. (WoW that was entirely too much B.s, I do apologize). As the cab air temp drops so does the suction pressure but before you start adding refrigerant try to get the cab in the lower 70* range unless the pressure is really flat. Adding just enough refrigerant into the system keeps from overcharging it when first recharging with high cab temps.
One thing that needs to be done to properly charge the system is to place a fan in front of the grill to simulate at least 35mph running down the road. If you do not have sufficient air moving across the condenser,the heat that is absorbed in the cab(causing the cold air discharge) and thru compressing, is not dissipated properly. The refrigerant metering device is an orifice tube. refrigerant comes out of say a 3/8" accumulator tube then it changes state to a cold refrigerant as it is pushed thru a fractional tube with a screen.By not having enough air blowing thru the condenser (vehicle just idling),the discharge/high side pressure will be much higher than normal. This high discharge pressure will directly affect the low side pressure causing it to also be higher than normal. Refrigerant have bubble and dew points(vapor and liquid) and to properly operate they must be at proper capacities, flows and temperatures. The engine should normally be sped up to approx 2k(same as alt electrical testing) to obtain proper refrigerant flow as well. You can watch the suction/low side pressure drop as well as shorter compressor cycle time when the compressor is operating at proper speed.
Gauges should always be used to properly charge a system but airflow thru the condenser is very critical.
I do apologize if this sounds like a "know it all" type response but it is just meant to give some important information.ostwhore2:

 

[Pwrcummins]

That was a lot to read lol. Thing is my compressor stays on. Won't shut off unless I turn off the ac.

 

[Lethalthreat7.3]

Sorry about the long post but here is another, I am trying to help those that really want to understand how an AC system works.
The refrigerant process is basically 4 steps, Hot Vapor, Hot Liquid, Cold Liquid and Cold Vapor. Each component works with these refrigerant states.
HOT VAPOR- the compressor compresses the refrigerant making a HOT VAPOR that is sent to the condenser.
HOT LIQUID- the condenser makes the refrigerant change state form HOT VAPOR to HOT LIQUID by rejecting the heat and causing it to condense.(this is why air is required across the condenser).The HOT LIQUID refrigerant is sent to the accumulator. This contains the desiccant and allows for a "tank" for the refrigerant to gather.
COLD LIQUID- the Hot Liquid refrigerant is pushed thru the orifice tube/metering device and this causes it to change state to a COLD LIQUID. This is a very critical point. The refrigerant must be sufficient enough to partially fill the accumulator and MOST of the evaporator. The evaporator/A-coil located in the fan housing must be properly flooded but not over full so that the final Cold Vapor stage can complete.
COLD VAPOR- the a-coil is almost completely flooded with Cold Liquid refrigerant that absorbs the heat from the cab allowing the cold discharge air. The absorbed heat causes the refrigerant to change state flashing off to a COLD VAPOR in the last pass/tube of the evaporator. This COLD VAPOR returns to the compressor which cools it and the cycle continues.
(Almost Done) . In a txv system(thermo expansion valve), the metering device has a sensing bulb which "opens and closes" the refrigerant flow to maintain a properly flooded evaporator. (This is important to know, I promise).
Refrigerant charge is extremely important but much more so in an orifice tube system because there is no way to "meter down" or "meter up" the flow, it is a "fixed" hole size. If the system is undercharged the evaporator isn't flooded,the delta T(temp drop across the coil) will be low meaning a cool not cold discharge air and the compressor will be forced to run hot causing premature wear and failure. Low charge also causes frequent "on/off" compressor cycling.
If the system is overcharged pressures will be very high, compressor may try to run constantly(older systems don't have high pressure cut outs. I remember seeing 415psig on a 1992 7.3 at idle in 1992) which can cause leaks, blown o-rings and hoses. An overcharge overfills the evaporator not allowing the proper change of state for cooling and allows liquid refrigerant to migrate to the compressor. We all know that liquids just don't like to be compressed, bad things can happen.

So. I truly rambled on for awhile here and you know more about the AC system process than you ever care too, BUT, I kept your attention this far.

Thank you.ostwhore2:

I have more info if there are questions you might want answered specifically.

 

[Pwrcummins]

Made a lot of sense good to know how it all works. Ac systems can be a pain. Lol

 

[Lee]

Do any power strokes have the Thermo expansion valve system?

 

[Fordguy100]

Excursions have a rear expansion valve, but the front system uses a orifice valve.

 

[Pwrcummins]

So the ac worked really well this morning around 5:30. Sun wasn't out yet. Does a black truck may have something to do with the cool air?

 

[Lethalthreat7.3]

Black absorbs more heat so the interior will get hotter than say a white color that reflects the sunlight which equals less thermal gain.
You said your compressor stays on constantly and never cycles off? This would indicate an overcharge.
The compressor cycles off and on via the low pressure switch. When load is high the suction side will be higher and this engages the clutch. As the vehicle cools, the load decreases and the low side/suction pressure also drops. The low pressure switch will cycle the compressor off and on.
If the charge is low you will have little cooling and the compressor will cycle on and off quickly. Cycle time also shortens as the interior heat load decreases.
If a system is overcharged it can cause constant compressor operation resulting in high pressures and low or no cooling capacity.
A sticking low pressure switch can also cause constant running.