A/C Pressure Issue

[Diesel Thunder]

As is common, my passenger side a/c vents are consistently 15-20 degrees warmer than the driver side and the only way to cool the cab is with recirculation mode. I have no problems with door settings as all of the selections work. Under the hood, my lines going into the cab are very cold with the smaller diameter one quickly frosting over with the a/c cycling. So I'm thinking I'm a little low on refrigerant. I haven't had any issues with evaporator freezing--that I know of.



So I decide to buy the low side pressure gauge with the trigger for refrigerant addition that so many on here have discussed.



So here are my readings.



To start, with a/c on max cool my initial readings are:



Compressor off = 30-40

Compressor on = 5-20



So I added the 3 oz can which includes: 1 oz. R134a, 1 oz. PAG100/ICE32, 1 oz. dryer, I also added approximately 6-8 additional oz. of R134a



I did NOT add any leak detector/sealer.



Now, with a/c on max cool my readings are interesting. With the max cool on, my low side pressure oscillates slowly between 40-55 with an occasional drift to the 20's. However, the compressor is not kicking on/off during the oscillations, and the cab is quite cool with only a 10 degree difference driver/passenger.



If I turn the a/c off in the cab, my pressure is 100-110 on low side.



Any thoughts?

 

[Crunch]

I'd say you need to take further diagnostic action with the full gauge setup. The device from Walmart will only tell you what your low side pressure is and function as a dispenser. The 03DRM. PDF file lists several reasons why the low pressure side can be high while the A/C is on, but that doesn't apply when it is off. Just from looking at your post that 55psi is too high. Your truck is from a different model year, but I'm guessing pressures should be similar. The low side pressures according to the repair manual should be 35 to 45 psi at 100*, and 40 to 50 psi at 110*. Your problem could be anything from an overcharge, to a slipping belt to air in the system to a compressor problem. If you have a Harbor Freight near by you can get the full set of gauges for around $40. But for anything other than a simple low side pressure check and quick fill with the Walmart device I'd take it in to an A/C shop for a full diagnostic. $50 to have them look at it and do it right is far better than thousands of $$ to repair it because you did the wrong thing.

 

[Diesel Thunder]

Thanks for the advice. I guess I'll head to my local Dodge dealer--they seem to be pretty good. They are advertising $59 for evac/recharge svc. Any recommendations regarding any requests for the mechanic?



ie:

-Vacuum Time/Inches?

-Recharge amount? 1 lb. 14 oz. vs. 2 lb. used by some here on TDR?

-Add ICE32?



I really don't think I have a significant leak problem as this is the 6th summer season since new and only last summer and this one have given me any indication of a/c issues. So I'll tell them to add dye, but no leak sealer.



How does this sound?



Thanks for your advice Crunch.

 

[jelag]

With the A/C off the pressure equalizes from the high side to the low side... so a high reading on the low side when the system is off, is not an issue...

Also, the amount of R134A won't change the reading from the drivers to the passenger side. . there is only one evaporator in the cab and the blower pushes air across it where its cooled... the blend doors are what controls the flow from one side to the other... if one door is not opening correctly or you have a dual control system more air is moved one way than the other... slower moving air means more heat is absorbed as the air flows from the evaporator to the register...

I don't have enough information to tell you if your still undercharged... usually a sign of being over charged is the flooding of the return line to the compressor and ice build up on that line... an excessive amount of freon goes through the evaporator and the portion that is still a liquid or hasn't absorbed enough heat exits the evaporator and chills the discharge line until ice forms...

Usually with the system on high in the recirculation mode you will usually see air temperature in the mid 40's - 50* when the system is working...

Also a good gauge set will give you the low side pressure... . on that low side pressure gauge is a temperature scale for different gases, and the scale for R134A will give you the temperature at the evaporator coil... this is nothing more than math...

Does this help...

 

[Crunch]

What I've heard about A/Cs is all over the map. When my truck was 3. 5 years old I took it to the dealer because it wasn't cooling like it was the previous summer. They did the recharge and I was on my way. They said it was normal for some blow-by leakage. Earlier this year Manny, Moe and Jack had a $50 A/C special going on so I stopped by because cooling efficiency had dropped again. They told me that the $50 was *only* to diagnose the problem, and that fixing it was extra. I told them what the dealer had told me years before, but they insisted that it's a closed system and if it was low there was a leak and it would cost extra. So I left. A friend with the same year truck said that a Dodge dealer told him that there was a design flaw in these systems that vented a tiny bit of refrigerant every time the engine started, whether the compressor was engaging or not. I mentioned this to another dealer when I was having some unrelated work done this last Spring and he told me that it's because the compressor is positioned so low, instead of above the engine. Not being an HVAC guy I can charge the system and read a simple gauge, but beyond that I'm just hacking around. I know A/Cs are supposed to be a closed system, but I also know that seals wear out and that bursts of high pressure can result in some blow-by. It sucks, but it's hard to trust anyone when it comes to diagnosing and repairing your A/C because everyone sees an opportunity to make a quick buck off the owner. So I go with the advice of a friend: If you have to put a $10 can of refrigerant once a year for the remainder of the vehicle's life it's still better than spending hundreds on something that may or may not be a permanent fix. If you are putting a can in more than once a year then your problem is something else and it's probably worth getting the major diagnostic and decide on a repair at that point. I know my compressor is working, none of my doors have broken (yet) and the only thing I've noticed is that roughly every 3 - 3. 5 years on a 7 year old truck I need a can of refrigerant. I can live with that and I'll just make sure I don't overcharge the system, and try to keep the low side pressure right in the middle of the range on the hottest days. As with oil, it's better to be slightly low, then slightly high. Especially in a state like Texas where we can see a lot of days over 100* every year. I'm thinking doing that will keep the pressure below max, even on the rare days where it gets to 110*+.