Air Conditioning and Sunroof Questions

[jmcgill]

I have a couple of questions that are pretty different....

First, my a/c works, but it is not cold enough. It feels to be about 50-55 degrees at the vents. It's a tad less cool when I'm going 70 on the interstate. Freon is charged, but the sight glass seems to show some bubbling at idle with the compressor on...at least it looks that way to me as it's a very hazy picture. I'm going to get a set of manifold gauges, and I took the EPA 609 test, so I can recharge it with R-12 if I need to...but I don't want to charge, if it's already at good pressure.

Is there anything else that might cause a lack of coldness in the AC?

Second, my sunroof works great but when I open it, I get this long rod that appears in my trunk and pushes away the plastic molding/cover on that side of the trunk. Is there some part I'm missing here that guides this rod?

Thanks,

Joe

[leathermang]

You are willing to buy a set if gauges.... but not a pencil thermometer to set into the vent so you can report the actual vent temperature instead of your ' feelings ' about the lack of cold ? It costs about $7 .....

Also, have you cleaned your fins both sides of BOTH the condensor and the radiator ?

Pretty much ignore the sightglass until you check out the pressures and other more dependable indicators. ( as referred to in the MB AC FSM )

It is prudent to check all the things out before sticking more R12 into the system ... an ounce too much will work your entire system very hard trying to cool you off... but will work just fine Several ounces " low "...... so always err on the lower amount side when installing or adding...

[280EZRider]

The rod in the trunk is probably the housing of the sunroof cable. It connects at the sunroof motor next to the antenna motor both under the plastic molding. It sounds like you are missing a bracket that holds the housing down.

You can remove the molding by removing 1 plastic nail, then the plastic housing it slides into, then carefully lifting & slightly bending the molding while lifting it out.

[jmcgill]

Pencil gauge shows 52 at the vents on the dash.

Condenser is clean on both ends. Radiator is new.

I'm going to get the gauges as soon as I can. I'm not sure how much pressure is in it. When I got it the compressor wouldn't switch on. I (after getting the EPA Certification) put about 8 ounces of R-12 in the system which got the compressor to come on and the air blowing colder than ambient. I had hoped it would cool off as the car ran more. I'm no pro, but I'm not stupid either, which is why I wanted to test the pressures before I put more R-12 in.

[tyl604]

Do not quite understand Leathermang's comment. I have always heard that bubbles in the sight glass mean you are low on freon, therefore you need to add freon. (I also seem to remember reading something in the forum lately, probably within the last 2-3 weeks, that said you add freon by weight and not by pressure but that might not be correct.) You might want to do a forum search to clear this up.

I do not know how much a 300D holds but I just had freon added to my 81 300SD. It was cooling but not quite enough. The indy added two pounds and said that the 300SD actually holds a total of 3.1 pounds which is quite large.

So maybe 8 ounces is not nearly enough. But then again I do not know about the 300D.

[leathermang]

So, tyl604 , Since you do not understand MY statement , and you have HEARD that bubbles mean to add freon you SUGGEST , WITHOUT looking at the MB AC FSM which I reference, that he add freon.

I SUGGEST that you do not know enough about Automobile Air Conditioning to be suggesting anything to other unsuspecting members of the forum.

[leathermang]

jmcgill, You are on the right track in using the vent temperature and getting the gauges to test pressures before further action.

Remember when you set up with gauges that you want the windows open, AC on Max, and some kind of forced air from the front of the vehicle... a squirrel cage fan works great blowing into the radiator. Notify us when you get ready to do next stage.

It is possible depending on your car that ' intervening variables' are at work... a messed up temperature sensor inside the car, things like that... but checking the pressures are the first thing....

The larger question is how did it get low on freon , if that is the cause...
have you checked for a leak ?

[HammerWerfer]

jmcgill, When testing the pressures in an A/C system, it is best if you have the engine RPM up around 1500rpm. This better simulates the going down the road conditions the A/C compressure is expirencing. At idle, the compressor is not pushing out the gas fast enough to give a stable and accurate reading

HammerWerfer

[tyl604]

Leathermang - you are exactly right, I do not know a lot about air conditioning but I am always willing to learn. I do not know whether or not you have the appropriate AC background (it would help if you would say that you are a professional mechanic or perhaps AC professional) but if I have a chance I will call my indy and ask the specific question.

Not sure why you seem so upset. The point of this forum is to learn.

Remember we are all friends here trying to help each other out to the best of our ability. No egos here.

[jmcgill]

When I get my manifold gauges, I'll do the whole setup like Leathermang suggested.

From what I can gather, the car really never had its AC used since 2007. When I bought it it didn't work, but I KNOW (via shop records) that it was leak tested, evacuated, and refilled in 2006.. Now that might mean that things have dried up, seals cracked etc, etc. since then....I really don't know, nor do I have $500 to pay for a shop to inspect the whole system right now...especially since I need engine mounts.

[leathermang]

Originally Posted by tyl604

Leathermang - you are exactly right, I do not know a lot about air conditioning but I am always willing to learn. I do not know whether or not you have the appropriate AC background (it would help if you would say that you are a professional mechanic or perhaps AC professional) but if I have a chance I will call my indy and ask the specific question.

Not sure why you seem so upset. The point of this forum is to learn.

Remember we are all friends here trying to help each other out to the best of our ability. No egos here.

Yes, I was upset and I will tell you why.

but first, to your question as to whether I am a ' pro' on either mechanicing or AC work. NO , I am not . I have only been doing all my own mechanicing for 40 years and only researched AC stuff about 6 years.

I own a CC text on HVAC, two books on Auto AC systems and I own the paper Mercedes Benz AC manual.

I would not tell you I WAS a pro even if I was because that alone holds no warranties .... we have had some CRAZIES post that were IN the AC business.

Everyone should evaluate each post for its logic and physics... not because of who posts it or what they claim to do off line.

The point of the forum IS to help other people with their problems.

It is not designed to be learning situation in which you give advice not based on good physics or logic and SOMEONE ELSE PAYS FOR YOU LEARNING IT WAS NOT RIGHT WITH THEIR MONEY OR TIME AND EFFORT.
****************************************************
Once I WARNED that the sightglass was not to be trusted ACCORDING TO THE MB manuals you had an obligation to check out that WARNING.
******************************************************
We should be trying to help others out to the best of our ability... but if your ability is limited, and your interest is more in the excitement of posting... as compared to the frugal , safe fix of the OP's problem...

Then the FRIENDLY thing to do is NOT POST... use other's posts who are careful about the OP's money, time and safety as a way to learn about that specific problem. Ignoring WARNINGS in the MB AC FSM, advising someone to possibly OVERFILL their AC system IS NOT FRIENDLY.

If you ask other people around here you will find that I ALWAYS get upset when someone RISKS other's money or time or safety without warning them that you have no actual facts to base your recommendations on.

I get even more unhappy if there is a body of evidence easily accessed which suggests the advice is ill conceived , dangerous, or illegal.
Greg

[Mercury]

jmcgill, does your electric fan work? Probably not much help at 70, but still a piece of the AC system design.

[71inka02]

Originally Posted by leathermang

jmcgill, You are on the right track in using the vent temperature and getting the gauges to test pressures before further action.

Remember when you set up with gauges that you want the windows open, AC on Max, and some kind of forced air from the front of the vehicle... a squirrel cage fan works great blowing into the radiator. Notify us when you get ready to do next stage.

It is possible depending on your car that ' intervening variables' are at work... a messed up temperature sensor inside the car, things like that... but checking the pressures are the first thing....

The larger question is how did it get low on freon , if that is the cause...
have you checked for a leak ?

So - in reading this...it states, air on max, squirrel cage fan blowing (never seen that done before), etc...etc... - So what's the differance in the 'new' automatic recycle/recharge machines and the 'old' style manifold gauges relative to measuring presure...? It's a closed system - right?

Now before you go deep in detail -- I understand the basics as far as the 'new' machine does it all - plug it in, hook it up, program it and hit start...

When I had my AC freon checked early summer on my 85 SD, the engine wasn't even running - They hooked it up, and pulled a vacuum - we walked around the shop looking at a couple of old BMW's being restored - an alarm sounded when finished with vac, they noted how much it pulled out, and then set it to recharge with the correct amount --

The machine sounded a 'finished' alarm -- They unhooked the machine - I cranked the engine, turned on the AC and it worked beautifully........

They charged me for the differance in the amount of freon removed and the proper amount used to recharge plus a small labor amount and off I went....

[Brandon_SLC]

Originally Posted by 71inka02

So - in reading this...it states, air on max, squirrel cage fan blowing (never seen that done before), etc...etc... - So what's the differance in the 'new' automatic recycle/recharge machines and the 'old' style manifold gauges relative to measuring presure...? It's a closed system - right?

Now before you go deep in detail -- I understand the basics as far as the 'new' machine does it all - plug it in, hook it up, program it and hit start...

When I had my AC freon checked early summer on my 85 SD, the engine wasn't even running - They hooked it up, and pulled a vacuum - we walked around the shop looking at a couple of old BMW's being restored - an alarm sounded when finished with vac, they noted how much it pulled out, and then set it to recharge with the correct amount --

The machine sounded a 'finished' alarm -- They unhooked the machine - I cranked the engine, turned on the AC and it worked beautifully........

They charged me for the differance in the amount of freon removed and the proper amount used to recharge plus a small labor amount and off I went....

That's the way my A/C technician does it too. Last 3 times I had a car charged (over about 12 years) the engine has not been running. Works like a charm. They only start the car afterwards to test the vent temperature.

I've also had a supposedly trained and certified technician install too much freon in my RX7. First time I climbed a hill on a hot day the system exploded. Filled the inside of the car with gas and fog, so needless to say I wasn't a happy camper. Luckily the invoice listed the amount of freon installed and billed. It was almost double what Mazda specified.

Once the manager saw that, he offered to pay to have my system repaired at the best shop in the area. They ended up loosing almost $500 dollars on the deal.

Moral of the story? You don't want to have your system explode!

[tyl604]

Leathermang - you make some good points.