HVAC issues...

[C0RR0SIVE]

I doubt we have anyone here familiar with HVAC, even fewer familiar when it comes to a car HVAC... Anyways, I have a truck here, check the sticker for the weight of R134A and it says "Left hand side, X.XX pounds, Right hand side, X.XX pounds" Both are ~2.0 pounds of 134, I have put around 3 in, yet the compressor never cycles on/off, it's always on no matter what weight, pressures check out just slightly high (about 10PSI on the low side, roughly 25PSI on the high side), and it finally starts putting out COLD air...

Do I have some sort of restriction somewhere? I am unsure of the exact weight the system needs because of that stupid right/left hand crap, as there is no "left" or "right" anything... :-\

 

[Joe C]

I was a hvac service tech for 20yrs, but not for automotive.
A quick google should get you close enough to run the a/c.

High side <200psi. Low side <50 lb.
"A good rule of thumb with R134a is to run fan on High with all windows open and engine at 1500 rpm. High side pressure in PSI should be about 2.2 to 2.5 times outside air temperature in degrees F"

What is the correct pressure on the high side and the low side of an efficiently working system

your gauges read the pressure/temp relation
the compressor should stay on until the temp inside the car is reached

 

[PP Mguire]

Has it sit a long while without any 134 in it? You might need to vac the system too.

 

[Joe C]

technically...if you got air into the system, you should replace the filter drier too. Not too likely that the system got totally empty to that stage. if it did then you have more problems than just a low charge. I can only guess, but right/left side might be referring to the hi/low sides of your gauges. you need to charge by pressure /temperature and not by weight

 

[C0RR0SIVE]

The system was busted open for approximately a month, I replaced the drier and vaccumed the system to ~-28.5PSI last night, and let it run for around 2 hours with the vac going to ensure max vac was pulled, and that all moisture was removed. I never thought about the left/right could be pointing towards the gauges, but why would it give weights instead of pressures to go via if it is that way? Not experienced enough to know about temperture/pressure relationships and all that fancy stuff, best I can do is weight and check pressures for typical values just to make sure something doesn't blow up.

Sometimes I wish I went to votech for HVAC.


I have come to the conclusion that I have a clog in the line, or multiple clogs... If I have a single clog, it is after the reciever/drier which makes things really tricky as the evap is right beside it, and difficult to access.... I think I will be renting a flush can, some flush solution and attempt to power flush the lines out to ensure there are no clogs... Sucks as I have to replace the drier again, but, oh well.

 

[Joe C]

A clog will give you excessive head pressure. (red high pressure gauge) and very low suction pressure. It's not uncommon to see a frost line on the tubing where the clog might be because of the pressure drop from that point.

from your first post, you state:

check out just slightly high (about 10PSI on the low side, roughly 25PSI on the high side), and it finally starts putting out COLD air...

from this T/P chart for 134a,
R134a Refrigerant Pressure Temperature Calculator


it states your low temperature @10 psi is only 6.67 degrees f and your high side @ 25 psi is 28.8 degrees f
How much refrigerant have you put in it? at 10 psi your evap coil would start freezing up on you, if your head pressure was high enough to do that...it isn't
If you can access the repair manual for your truck, it should state the amount of proper charge in lbs. if the system is in a vacuum state, then just add the number of pounds recommended by the manufacture into the system on the hi side ( a good vacuum in the system should pull in the most of the charge without even having to start up the truck), Don't forget the refrigerant oil, If the system was left open for any length of time, then the oil would have moisture in it too and should be replaced)
I would guestimate that your hi side @ a 75 degree ambient (outside air temp) you should have between 175 to 225 psi and the lo side should have about 30 to 40 psi
I'm not familiar with automotive a/c but I do know that your evap temp should be above freezing. A 30 psi evap equals out to be 34.6 degrees f

 

[C0RR0SIVE]

I didn't list the actual pressure earlier, only listed how far over on pressures I was. In total, head pressure spiked to nearly 300PSI at one point yesterday but came down slowly, low pressure sits around 55ish PSI. The truck currently has... (Shoots self in head, never doing this stuff with-out sleep again) way too much 134 in it, calls for approximately 38oz according to GM, i have nearly 60oz in it, was just too tired to keep count of anything, nor care, just wanted some cool air to come out of the thing.

I will evacuate it tonight if I can, flush the lines to make sure they are clear, remove the compressor and dump the oil (didn't know PAG could capture moisture easily), refill with the proper amount of PAG100, replace the drier, draw vacuum till it hits ~-29PSI, vacuum for another hour after it hits that point, then let it sit and hope it doesn't leak. Will refill after...

There is only one or two things I can not figure out about this truck aside from the current issue related to the AC... All air conditioners use either an expansion valve, or orifice tube, correct? Well, this truck appears to have neither?! The manual for the AC system on it lacks a lot of information that is usually found in it for other cars. I had hopes that it would have an orifice tube and be partially clogged as it would explain why my pressure readings are doing what they are doing, which seems to be semi-poor suction, extreme head pressure.

Le' Sigh, sometimes I rather take stuff like this to a shop, just don't wanna dump out $500-$1500 for a local shop to screw me.

 

[Joe C]

normal a/c's that have compressors that run at a constant speed do have cap tubes or txv (expansion) valves. A car engine does not run a constant speed so they have a pressure regulator type of expansion valve. Because of this, you can get close to the charge by weight and should be good with that because there are liquid line and suction line reservoirs to hold enough refrigerant to make up for the radical changes in temps and engine speeds that autos have. Take about 2-1/2 lbs of refrigerant out and see how that works, if you stick your 134a can in a freezer (low temp can will hold more refrigerant because it will have a lower pressure) you can take it out of the truck and put it back in a cold can. If you using one of those 1 lbs cans that you get at the auto store, then don't try that because you can easily over fill it and cause the relief valve to pop off, these relief valves are a one time thing, best not to try it... you could seriously get killed or even worse...just get maimed

 

[C0RR0SIVE]

I have a empty 60 pound tank that can be used for recovery purposes available to me as well as a 30 pound tank full of 134, and numerous little 12oz cans... The key issue that sort of lead me into putting too much in is because the compressor never could cycle on and off, it would just continuously run, like I said, I was tired. xD

I do have most all the tools and equipment anyone could ever imagine available to me for AC work when it comes to automotive systems.

Anyways, thanks for the ideas/help so far Joe, will post back tomorrow with how things go, as the truck is out and about today and wont be back here for another 8 or so hours.

 

[aembry]

I have a degree in HVAC and industrial maintenance, and its seems to me like you got your system over filled with refrigerant. I can't say for sure without inspected it myself but 99 percent sure you are about one third of the weight over where it needs to be. When there's to much it won't superheat and get at a constant level of pressure on the gauges so its working so hard to get cold that it will eventually start to freeze up then its not gonna get cold again until it thaws, so it basically won't be blowing cold air long once it gets cold. I am having some computer issues that's why Im on this site and it feels great to know a answer to something, although I'm terrible at explaining it I am in my element with HVAC or any kind of electronical issues. Its 5 am and I just got off work so I'm going to bed for a bit and if you need anymore advice email me at andyembry17@gmail.com, I'll check this site for a solution for my PC and try to remember to see if you posted any more questions on this subject, but if you need help email me and I'll try and explain the reasons better than I did now.