91 300d ac compressor replacement

[swampcop]

In the next few days I plan to replace my ac compressor as the clutch on the compressor froze. I have the new compressor and read the directions included with the compressor stating that the drier/accumulator must be replaced prior to the flush and recharge. How crucial is it that the drier be replaced? Once I have the new compressor in place I plan on taking the car to a shop to have them perform the pressure test, flush, and recharge. Should I just spring the loot for the drier or wait to see what the results are from the shop?

[engatwork]

If it is going to be opened up for any length of time you should replace the dryer. IIRC some folks won't guarantee the compressor without the dryer being changed out.

[hertfordnc]

I have no credibility here but I'll share my thoughts and recent experience.

I had two modern cars and a vintage RV that all needed AC charging. I cracked a line on my 06 Civic Hybrid and last winter i changed the compressor in my 01 Expedition.

It get's really hot here. I bought a case of Duracool and a AC vacuum pump and serviced both cars myself with excellent results.

The purpose of the drier is to remove moisture. From a sealed system in good order, opened briefly, i can not imagine that the moisture in the air would be enough to overwhelm the drier.

In my case, it was an acceptable risk. If it didn't work i'd only be out a couple cans of duracool.

Factor the cost of paying the AC guy twice and whether or not the compressor will retain it's warranty and consider the risk.

Or, drop $200 on a vac pump and hoses and gauges and do it yourself. It ain't rocket science.

[sixto]

The compressor innards froze or the clutch froze? You can replace the clutch, coil and/or bearings without discharging the refrigerant. I did it on an '87 300D which has considerably less room to work than your 2.5. If you don't like working blind, detach the compressor from the block and tip the clutch end downwards for more room. In my case, the radiator had to come out. In my case, a bearing went bad causing the pulley to rub some insulation off the coil. The fuse would blow whenever the compressor engaged.

If the system will be open, I'd replace the low pressure switch with a MB brand unit for good measure.

Sixto
87 300D^2

[Air&Road]

sixto is asking the key question here. How did it fail? If the problem is solely with the clutch and the compressor still rotates freely with no internal trouble, replacing the clutch is the only way to go IMHO.

If the compressor failed catastrophically, then debris is scattered THROUGHOUT the system. EVERYTHING must be thoroughly and completely flushed, breaking every connection. After everything is flushed clean, the flushing agent is THOROUGHLY removed the system and everything else is back together, replace the reciever last thing and be ready to immediately start the evacuation process. This way you can expose the dessicate to the least amount of moisture that it will have to absorb.

There's no reason to use any refrigerant except what was in it originally.

Hope this helps.

[hertfordnc]

Originally Posted by Air&Road

There's no reason to use any refrigerant except what was in it originally.

Hope this helps.

I was not suggesting he use Duracool, it works for me and it's a great option for R12 systems but the 91 has R134, right?. But i am suggesting doing your own service if the systems is not contaminated.

[swampcop]

The clutch on the compressor did freeze up, but the compressor was fine. I was able to get my mitts on a reasonably priced compressor so it made more sense to go for that rather than just the clutch. I planning on changing the dryer as I figure the $20 for the 22 year old part is worth it. A local shop is offering a deal on flushes/recharges, so i'm going that route.

[Air&Road]

Originally Posted by hertfordnc

I was not suggesting he use Duracool, it works for me and it's a great option for R12 systems but the 91 has R134, right?. But i am suggesting doing your own service if the systems is not contaminated.

No I think '92 was the first year for 134 in a 124 Benz and I don't think that all '92's got it.

All alternative refrigerants such as Duracool fall into one of two categories; flammable or blend.

Many people feel comfortable with flammables in spite of the fact that as of a few years ago they were illegal for mobile refrigeration in 18 states.

Blends are just that, a blend of two or more components. One of the components is usually there for it's cooling capability and the other component is there for it's ability to circulate lubricant.

Blends will work, but there are several down sides to them. First of all, a/c shops will not have a recycle/recovery machine set up for it. This means that they have to recover it into a vessel designated for junk and PAY to dispose of it.

Compounding the above problem is the fact that when a blend leaks, the components leak at different rates. This means that it can not be topped off, but must be dumped into the junk vessel and again disposal must be PAID for. THEN the system is recharged from empty.

I don't remember if Duracool is a blend or a flammable, but I AM sure that it is one or the other.

There are those people who prefer to use alternative refrigerants in spite of the fact that R12 has come back down in price. With R12 obtainable for $15 a pound or so in today's market, it's difficult to understand why anyone wants to use alternatives. The fittings alone might cost as much as any potential savings on refrigerant cost.

Anyone, of course, is free to do what they wish, but I just try to make sure that people are aware of the situation before jumping in.

Hope this helps.

[hertfordnc]

Aside form the discussion about refrigerants, it's neat to see the "cultural" differences between different forums. I also hang out on the GMC motorhome forum. We're a bunch of old shade tree mechanincs doing whatever we can to keep 40 year old campers going down the road. Backyard engineering is encouraged and shared. It's appropriate for that vehicle.

In this group we have maniacal devotion to authentic high quality repairs. There is a lot more reverence for the original engineering. (with good reason)

I think both points of view are appropriate to each vehicle.

Regarding Duracool; the GMC guys started using it and it has become standard practice. Along the way guys started using it in their other modern vehicles.

It is a propane butane/blend and it is illegal in a lot of places.

But it works great, is efficient at a lower pressure than the other refrigerants (less strain on older systems) and is compatable with R12 and R134 and both common types of oil.

I my case, i guess I'll bleed it off and replace it with R134 if i ever sell the cars i used it in.

[swampcop]

Last night I took the service plate from the old compressor and cleaned it up to transfer to the new compressor. Reading through the service manual(s) I found a few things that left me scratching my head:
1. What volume of oil is suppose to be in the compressor? One page in the manual states 120ml while another page states 140ml; and,
2. I know the compressor uses PAG oil. One place in the manual shows 'cold flowing oil.' Which type of PAG oil is used for the compressor?

Thanks!