A/C overcharged? high engine load, increased running temps, stalled...thx for input - Page 5 - PeachParts Mercedes-Benz Forum

leathermang · #61 04-04-2011, 04:15 AM

Marvelicious , You have been doing your research in the right places... you have correctly stated conservative industry wide opinions based on the physics of the situation. If everyone were willing and able to do that we would not have pages long heated discussions with people muddying up the waters and potentially causing innocent forum members huge unnecessary costs in both time and money getting cool air into their vehicle... ... You are a positive role model for everyone reading the forum. ( or any forum )...

vstech · #62 04-04-2011, 08:35 AM

Quote:

Originally Posted by Marvelicious

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.

33% eh? hmmm. I wonder how much capacity improvement there is, with the substantially lower volume of refrigerant in the system. perhaps a larger receiver dryer could be installed to compensate...

Marvelicious · #63 04-04-2011, 02:59 PM

leathermang: Thanks for the compliment, but I've always been better suited to being a bad influence than a positive role model. It is good to know I'm on the right track, even if it is a more expensive track. I plan on keeping this car for a number of years, so I feel like the best long term approach is going to include a r134a for future compatibility. I also see a Sanden in my future, but I will admit I have a prejudice against things that say Delco on them. GM's Achilles heel.

vstech: The thing about increasing coolant capacity is that you can only really use what you can cool. Having a "reservoir" of extra coolant on the cool side of the condenser would just give it time to warm back up before being used I think.

sshanky · #64 04-04-2011, 03:56 PM

I stopped at the shop today to tell them about the issue, and they wanted to schedule a slot for me so they can check it out. He told me he would want to evacuate and reload the system to ensure it is the correct amount. I decided to wait a few days till the weather gets hot and then have him check it, since it is quite cool out today and the system is working well and blowing cold. It hasn't been as hot as the day I posted the original issue since then, and I have not experienced the problem again.

Yak · #65 04-04-2011, 08:08 PM

Quote:

Originally Posted by sshanky

I stopped at the shop today to tell them about the issue, and they wanted to schedule a slot for me so they can check it out. He told me he would want to evacuate and reload the system to ensure it is the correct amount. I decided to wait a few days till the weather gets hot and then have him check it, since it is quite cool out today and the system is working well and blowing cold. It hasn't been as hot as the day I posted the original issue since then, and I have not experienced the problem again.

Not to throw a red herring into the mix, but there's the possibility that there was residual moisture that froze up in the system (TX valve, maybe?) that has subsequently been removed by the dessicant in the dryer. Or the oil needed time to work it's way through the system.

With the fan running, it'd be a good idea to get the pressures checked regardless. Maybe also see if you've got the Hi+Lo pressure switch installed prior to evacuating. $20 ish @ Fastlane.

<<http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1979@@1979&makeid=63@@MERCEDES+BENZ@@X&modelid=6203%3AED%7C10000133%3AMBC%7C1509@@300SD&catid=242213@@Climate+Control&subcatid=242239@@A%2FC+Pressure+Switch&applicationid=W0133-1628267@@A/C Pressure Switch&mode=PA>>

sshanky · #66 04-04-2011, 09:01 PM

good idea. Thanks. I am going to order the valve and have him put it in when he checks the refrigerant level for me. Thanks for pointing out how easily I can get the hi/lo valve!

It was only 79 today and the A/C worked great, but when I shut it off, it made a really strange sound. I want to try to capture it and post it when I can...

leathermang · #67 04-04-2011, 09:39 PM

I do not think Yak was throwing in a red herring.. I think there is a good chance of that.. you are getting excessive WRONG build up of pressure ( we assume based on the reported effects on the engine ).... moisture in the system could cause that...
You have to put some gauges on it !!!! Don't order the valve until you have put gauges on it...
If they " Reload ' the system they get a second chance at vacuuming the moisture out..and you are likely not ever going to know the actual cause of the problem if they are in charge of the next procedures...
but I understand that they should fix what they did not do correctly...
but people on a DIY forum want to know for sure what is happening.... and why...

leathermang · #68 04-04-2011, 09:53 PM

Quote:

Originally Posted by Marvelicious

...vstech: The thing about increasing coolant capacity is that you can only really use what you can cool. Having a "reservoir" of extra coolant on the cool side of the condenser would just give it time to warm back up before being used I think.

OOOOPPPPSSSSS.. may have spoken too soon....LOL
You appear to be visualizing two different parts and using one cooling concept for the both of them...
I have long advocated increasing the cooling capacity ... the volume between half way down the condensor and the TXValve... the high side of the system.. where the coolant which has had " work " applied to it... increased the pressure and cooled it in the condensor... is stored ready for being sprayed into the evaporator to cause the heat to be absorbed from the air passing over the outside of the evaporator...
I thought one cute trick for doing that AND providing a way to change out receiver/dryers without having to evacuate and refill the system was to install parallel receiver dryers and ' rotolock ' valves connecting them to the system... this would add the capacity of the receiver dryer to the system...and mean you could rotate on a regular basis new ones in with just a few simple moves....
But back to the point... as long as that ' work ' has been done to that vapor exiting the compressor.... it is available for changing to low pressure in the evaporator and doing the job the AC is designed to do... adding capacity there has the advantage of doing the ' work' when driving at normal speeds as an example...and USING that STORED Work product at STOP lights and crawling traffic speeds ( until that reserve is taken up..then you need the regular things like the aux fan, clean fins on condensor and radiator , fan clutch working on those cars that have them ( mine does not )...
Not a fatal mistake.. hang in there.. it is not easy visualizing the workings of a dynamic system with all its physics variables changing all the time.....

vstech · #69 04-04-2011, 10:07 PM

Quote:

Originally Posted by Marvelicious

vstech: The thing about increasing coolant capacity is that you can only really use what you can cool. Having a "reservoir" of extra coolant on the cool side of the condenser would just give it time to warm back up before being used I think.

not exactly. once the liquid has passed the condenser, the liquid volume has had the excess heat removed. now the gas from the compressor is pressing on the system, and the evap is a large negative pressure area. the larger receiver will allow the improved performance of the parallel flow condenser to store the cooled liquid for flow adjustement. a larger reciever allows more of a buffer of cooled liquid refrigerant to flow when demand (inside heat and outside heat) are needed.

leathermang · #70 04-04-2011, 10:17 PM

Quote:

Originally Posted by vstech

not exactly. once the liquid has passed the condenser, the liquid volume has had the excess heat removed. now the gas from the compressor is pressing on the system, and the evap is a large negative pressure area. the larger receiver will allow the improved performance of the parallel flow condenser to store the cooled liquid for flow adjustement. a larger reciever allows more of a buffer of cooled liquid refrigerant to flow when demand (inside heat and outside heat) are needed.

I just said that !!!! and I used a LOT MORE WORDS.....

Marvelicious · #71 04-04-2011, 10:40 PM

Right, as soon as I started reading through your posts, I realized my mistake. Its the phase change from liquid to gas that actually cools the evaporator: like why your barbecue tank ices up. Bigger receiver = bigger barbecue tank = more capacity to cool when the compressor isn't working at optimum - say at an idle just after starting with a hot car thats been sitting in the sun all day. The compressor and condenser have the job of resupplying the system.

I'll get this stuff yet...

vstech · #72 04-04-2011, 10:43 PM

Quote:

Originally Posted by leathermang

I just said that !!!! and I used a LOT MORE WORDS.....

tis the true expert that can confuse/ explain in the fewest understandable words!

sshanky · #73 04-27-2011, 02:41 AM

I don't know if anyone is still watching this thread, but I bought some r134 gauges at harbor freight. I know, they're cheapos, but how often will i really be using them?

Now, I have to figure out my strategy. The shop guy will be happy to check the level for me and re-load the r134. I also bought a high/low pressure switch that he could put on if he did that...whether or not that's a good idea, I don't know.

I can play around with the gauges, if you guys think I should, and see what the readings are (will I lose r134 that way?). I remember a lot of you mentioned that gauges would help solve problems.

leathermang · #74 04-27-2011, 03:10 AM

Yes, put the gauges on after you have made sure you understand what the test conditions must be....
You will lose almost no refrigerant...only that in the hose line..... and you need to have the top fitting a tiny bit loose until you have put some refrigerant into it... and then when you hear some escaping tighten it down... that is called purging the line... ( of air )...
" how often will I be using them "... sorta of a funny thought... so the possibility of not getting the correct readings perhaps the only time you will use them is comforting ?
LOL

They will probably work just fine...

Find Vstech's description of the criteria for test conditions...

leathermang · #75 04-27-2011, 03:12 AM

The shop guy can check the ' level' of what ?
You mean he can confirm your pressure readings ?