AC not cooling well

BG1 on Thu September 16, 2010 7:07 PM

Year: 1976
Make: Pontiac
Model: Firebird
Engine Size: 455
Refrigerant Type: R134a
Country of Origin: United States

This ac has had the R134a in it for several years and a hose started leaking so I opened it up to take care of that and also thought it might have gotten moisture in the system so I thought it might be a good time to try re-calibrating the VIR also. It was not cooling good and the pressures were off, the low was around 30 and the high was 275-360 and the best vent temp was 54 degrees.
The VIR I have is the EEVIR and I re-calibrated it and put it in today but I am not finished. I had a hard time getting the r134 into the system but it has about 38 oz in it. The vent temp is poor, its only about 62 degrees and I am not sure if more r134a would help or not? The line that goes from the compressor to the VIR is frosting over at both ends and I am not sure if its supposed to do that? The line from the evaporator is cold but not frosting and the top of the VIR is barley cool. The outdoor temp was about 80 degrees today. What do you think?
I added some r134a and it should be at the max amount. The best the temp got to is 54 degrees and it would increase temp with the engine rpm. The temp outside was about 92 degrees and the low pressure was at 32 and the high pressure was 235-250. Sometimes the suction line would have frost on both ends and sometimes it was barley cold, sometimes the top on the vir was cold and sometimes it was barley cold. Before I made these changes the best with the r134a was 54 degrees but I think there was moisture in the system and I did not know how much oil was in it. I think the pressures are better now but the results are still off. I tried to unplug the thermal limiter and I think I damaged it because a little while later it blew so I need to pick up a new one. These results today were without the thermal limiter in place, I had a jumper wire on it.
Today I installed a new thermal limiter and tried the ac again and the outdoor temp was 80 degrees and the low pressure was 26 and the high was 180 with a vent temp of 56. The temp went up with the rpm. The suction line was cold at both ends, the top of the vir was cold, inlet and outlet of the evaporator were both cold. The new desiccant bag was in a plastic bag that did not appear to be vacuum packed and some I have seen were vacuum packed. I did not take very long to install the bag and close the system up and pull a vacuum for about 3 hours, I do not know if this could be part of the problem. I checked the static pressures today the outdoor temp was 78 and the static low was 82 and the static high was 90. I was told that these pressures may indicate moisture in the system.

BG1 on Fri September 17, 2010 1:04 PM

TRB on Fri September 17, 2010 2:28 PM

Your pressures seem to indicated a undercharge of the system. That and the r12 charge for this vehicle was like 60 ounces.

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BG1 on Fri September 17, 2010 4:42 PM

I thought that the system held 3.25 lbs or (52oz)? As I said in my post I increased the amount of R134a from about 75% of what I thought it held (38oz) to about (50oz). So it sounds like I need to add more R134a? What should the static pressures be? Does it sound like the desiccant bag was ok? It was in a sealed bag just not vacuum packed.

TRB on Fri September 17, 2010 6:29 PM

Personally have no clue what the static pressure should or shouldn't be. For me the only thing static pressure shows it there is some refrigerant in the system.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Tennessee_Timmy on Fri September 17, 2010 9:28 PM

Quote
Originally posted by: BG1
I checked the static pressures today the outdoor temp was 78 and the static low was 82 and the static high was 90. I was told that these pressures may indicate moisture in the system.

If I understand everything that's been said on here for the last 5 years, then, for an ambient temperature of 78, even if you're undercharged as all get out, but there is 1 ounce of liquid refrigerant in your system, you should read around 82 psi. On the other hand, if your system is completely charged and freezes you out, you'll read ... around 82 psi.

Even knowing that, I still catch myself reading more into static pressure than I should.

As the Tim who actually knows something said: "For me the only thing static pressure shows it there is some refrigerant in the system"

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Good Luck 2 ya,
Timmy

wgabriel10 on Sat September 18, 2010 10:10 AM

I am surely no expert on the subject, and will surely agree with the advice given. For example, in my recent compressor change when I recharged the system, I made sure I used the correct charge of refrigerant by weight. The pressures looked "nominal" to me. Truthfully speaking I did not even write them down and don't remember what the were to any degree of accuracy -- after all, they vary so much for lots of reasons. It seems especially hard to me to think of what the pressures "outta be" when running the vehicle sitting in a carport with the hood open, variable clutch radiator fan, engine heat going who knows where, a myriad of ways for air recirculation, etc. You can see a significant change in pressures just by lowering the hood or spraying some water from a spray bottle into the front of the vehicle on the condenser coil. Actually that can be a bit of an indicator of what you might see when driving.

What was most important to me was to get the vehicle "on the road" and see what differental temperature I saw between evaporator inlet air and air duct outlet in the vehicle. I was seeing 28 to nearly 30 deg-F at cruising speeds and engine around 1500 rpm or so. Of course this differential dropped off some when slowing down or stopping for a traffic light, etc. If I remember correctly, about a 30 deg-F differential is as good as you can get in typical automotive a/c systems.

I've always wondered why you cannot find "pressure vs temperature" charts for vehicle a/c systems like manufacturers provide for home a/c and heatpump systems. The charts do help; however, I have found that there is lots of variance between what you find in an installed system versus what the chart says. So, even in home systems, you want to look at return air temp versus cold duct outlet as one of the best indicator of system performance. In testing home systems, you even need to take into acount the relative humidity for some measurements. Some are "wet-bulb"; some are "dry bulb" measurements. There are so many variables to take into consideration in a/c system performance, it's no wonder that we "stay confused"! LOL!

So, the advice in the by-lines of a number of the pro's here, saying that Numero Uno is knowing what the refrigerant charge is and that the only way of knowing the charge level is to start from scratch, is surely is great advice.

And for sure, situations where a retrofit from R12 to R134 has been made creates a whole new game. I have an old truck that I need to do that to myself and almost dread doing it.

So much for my "editorializing".....I do hope you get it fixed, BG1.

Watson