A/C overcharged? high engine load, increased running temps, stalled...thx for input - Page 4 - PeachParts Mercedes-Benz Forum

leathermang · #46 04-02-2011, 08:56 PM

Quote:

Originally Posted by 79Mercy

Yes, but the OP is having a problem with the compressor putting a excess load on the engine, not the evap freezing up.

EDIT: i fixed the picture

If you know what the problem is definitively.. Just TELL the OP...

I am just trying to figure out all the possible ways in which the system can be loaded to excess and cause the symptoms noted...

79Mercy · #47 04-02-2011, 09:00 PM

I do not know exactly what the problem is with the system, never said i did. We need to figure out what the system pressures are, I think that would answer most of our questions.

That noise you hear when shutting off the car sounds like the AC compressor clutch to me. What do ya'll think?

leathermang · #48 04-02-2011, 09:04 PM

I have already mentioned to the OP that he is going to need to put a set of gauges on his system to logically go much further with this quest....

leathermang · #49 04-02-2011, 09:34 PM

Quote:

Originally Posted by engatwork

should have stuck with r12

I wonder if they even asked him if he had a preference..
Some places no longer have R12 equipment..
so would just go ahead and do the changeover to get the work....

leathermang · #50 04-02-2011, 09:37 PM

Quote:

Originally Posted by engatwork

this thread is worthless without pressure readings.

That seems a little harsh... I expect some amount of theory and insight into chasing down AC problems has passed to some people... hopefully...
Threads are not just for the OP... otherwise all would be conducted via PM...
seeing how these things are chased down can be helpful....

engatwork · #51 04-02-2011, 09:57 PM

It sure would be nice to see some pressure readings

.

If the system was properly cleaned and there were no particles of metal left in it then I suspect we will see elevated hi pressure readings when the engine loads up. I also suspect that the elevated (but not out of range) engine temp is because of the compressor loading the engine up. I'm also thinking that alot of what you are seeing is because there is r134 in a system that was designed for r12.

sshanky · #52 04-02-2011, 09:58 PM

Hey guys, thanks for all the information. I'm interested in both how to solve the problem I am having (and finding out whether or not i even do have a problem) and learning how the system works. One of the things that I was especially interested in, additionally, is understanding ALL of the ways the compressor can be made to shut off (i.e. cycle, if it does cycle). The one that leathermang was wondering about is important to know about -- I guess it is the one switch I was unaware of that could affect the compressor. The other ones (the pressure switch and the cabin on/off switch, and the vacuum switch taht goes on when you hit DEF or BI-LEVEL, were the only ones I knew about).

I wish I could show you guys the load the compressor was putting on the engine when it was hot and I did the quick off/on thing. I'll try to get it to happen again tonight or tomorrow and post a video if it does.

Regarding the gauges, I guess I will try to go by the shop on Monday and find out how much he put in. What else should I ask? about oil? What can he test with his gauges for me?

sshanky · #53 04-02-2011, 09:58 PM

engatwork, do you think I should be leaning toward getting r12 back in this system? would that cost me an arm and a leg? can it be done after the system has been converted to r134?

engatwork · #54 04-02-2011, 10:02 PM

Get him to hook his gauges to it and provide the pressure readings while running at around 1500 rpm and get us those numbers. Make sure the engine is up to temperature when he does it too.

I would recommend studying one of the good a/c manuals that are out there to find out everything you need to know about how they work. It is a relatively easy cycle.

leathermang · #55 04-02-2011, 10:02 PM

I will be glad to answer that... and I am sure Jim agrees...
yes, you are probably looking at moving back to R12 in order , in Ariz , to have a nice cool working AC system... if the car AC had been engineered for R134a like new cars.. no.. but it was made to work with R12 and mostly in cooler climates... like Germany and Wisconsin..LOL

leathermang · #56 04-02-2011, 10:04 PM

Quote:

Originally Posted by engatwork

Get him to hook his gauges to it and provide the pressure readings while running at around 1500 rpm and get us those numbers. Make sure the engine is up to temperature when he does it too.

I would recommend studying one of the good a/c manuals that are out there to find out everything you need to know about how they work. It is a relatively easy cycle.

It is important when doing those things to have some kind of forced air system for the condensor air flow.. the bottle neck in ALL AC systems...
In addition to good books on Automobile AC...
there are some sites on general AC systems... like Aircondition.com... and ACkits.com ....
I am interested in knowing if they even asked you if you wanted it converted... mentioning that the R134a runs at higher pressures and is inherently less efficient before converting your system ?

engatwork · #57 04-02-2011, 10:07 PM

r12

The hard part is going to be finding someone to do the job for you using it. If you were local I'd be more than happy to help you out. I've successfully converted about 5 or 6 back to r12. If they put r134 oil in it when they converted to r134 then it is the same job as what they have already done. Flush everything out and start over. The compressor would have to come off to flush the correct oil through it. You have to get a epa license to purchase the r12 but that is simple enough. Do a search on it.

It is late here, I'll talk to ya'll tomorrow. Keep in mind the a/c cycle is pretty straightforward but you have to do it properly to make cold air. It is as important here as it is in Az.

leathermang · #58 04-02-2011, 10:09 PM

Yes, he can do it himself ... and he seems to be mechanically inclined anyway...
the EPA test is OPEN BOOK... ONLINE...and ( last time I checked ) about $20 ....
they just want to know that you know how to deal responsibly with the refrigerant with respect to the environment...

Yak · #59 04-03-2011, 11:58 AM

My experience with trying to get a shop to do R-12 may be relevant. You'd be hard pressed to find a new compressor that will permit R-12 to be installed AND still be warranted. Since 134a is the "replacement" for R-12, and the CompressorWorks compressor says "for 134a" and to use PAG oil, then the shop was basically meeting the requirements to warranty the parts used to do the repair.

The CW compressor may also have a lifetime warranty, so hold onto the receipt.

The prices look reasonable. Not rock bottom, but fair enough. The shop did state a flush of "debris" from the system and replaced the right parts, so the repair seems okay with the exception of them not fixing the fan.

That factor alone would make it very hard for them to measure the proper cycling and cooling.

The red cap is a picture of the 134a high-side port, so they can measure the system pressures. I've attached a link that compares the pressures from R-12 and 134a. http://www.ackits.com/aacf/ptchart.cfm

The R-4 compressor was designed for R-12, so it doesn't work optimally with the higher pressures of 134a. Higher pressures = more work = more drag on the engine = higher coolant temps = less efficient cooling due to the proximity of the radiator. This doesn't even consider the lower efficiency of the 134a compared to R-12, so yeah, R-12 is better in this application (but see above for possible reasons the shop went with 134a).

Now that your fan is working, I'd recommend taking it back to the shop and getting them to check out the pressures.

A good wash of your condenser and radiator may also help.

Marvelicious · #60 04-03-2011, 01:44 PM

Quote:

Originally Posted by sshanky

engatwork, do you think I should be leaning toward getting r12 back in this system? would that cost me an arm and a leg? can it be done after the system has been converted to r134?

I've been doing a lot of reading on this stuff lately, but I'm no expert. It sounds like you are dealing with the same symptoms that plagued the previous owner of my car. The compressor seized when I was checking it out to buy, so it knocked quite a bit off my price. According to maintenance records, this car was "converted" in the same way yours was, and the previous owners did mention it ran hot in the summer. Since I got rid of the A/C belt it runs cool.

To sum up, I'm interested in this thread because we're in the same boat. Difference being, I'm in a colder climate.

What my reading is leading me to believe is that if one expects this older system to work more than marginally well on 134a, the factory condenser on this car isn't really up to the task. The estimates say that 134a is roughly 20% less efficient than r12. Other estimates I have read say that a modern parallel flow condenser is around 33% more efficient that our old fin and tube style. Now I understand that the condenser is only one link in the chain, but to me it seems to be the most essential part - shedding the heat - especially in a climate like your's where the temps are beyond what the system was designed to cope with even when new. As the outside temps hit that 100 degree mark, having the extra capacity to get the heat out of the coolant could only be a benefit even with r12.

Granted, if your system was overcharged (like it sounds like it may have been) this info will have no bearing on what it takes to make it work.