A/C Fix You May NOt Need A New Compressor

DanG144 · Nov 17, 2013

Good question on the flushing. I do not know for sure, but I used mineral spirits followed by acetone - the final flush with acetone which leaves no residue. The 90% alcohol is 10% water. And having the system water free before you start adding refrigerant is one of your major goals.

That being said, I have no idea what the normal flushing fluids are - no idea what a professional machine would have in it.

colinstone · Nov 18, 2013

Looked a data sheet - isopropyl alcohol and heptane 80/20.

Have some methylated spirits and acetone, so will use those.

Anyway, the fun continues. Got the pressure switch off - fitted very tighty and no evidence of any lubricant when originally assembled.

Unscrewed the schrader valve and it has come apart - thread portion, rod and spring have come out leaving the rubber sealing bit on the pipe. Dribbled in a bit of plus gas and hopefully tomorrow I can use a self tapper to pull the remains out.

I guess the schrader valve is not essential and if the pressure switch needed to be changed again, the system would have to be degassed.

tetragrahamaton · Mar 17, 2014

Another happy TmpaFL2000Dsl customer here. Suspected RCV failure on my '02 wagon, local shop had never heard of an RCV and said I needed a new compressor. Emailed him after reading the other feedback in this thread and he made time for me to drive down this past Saturday. He walked me through the whole diagnosis, opening up the valve cover, etc. (Also discovered that the local shop hadn't bothered to return my refrigerant after the inspection!) Turned out my compressor was totaled after all (it was a cheap Autozone / Compressor Works unit that came with the car, and a couple of the valves were mashed to bits), but he told me about a local scrap yard where I was able to pull a working OEM Sanden for just $40. Lent me the necessary tools and everything. A/C works great now, and I saved at least $400 and received a ton of free knowledge and advice. Thanks TmpaFL2000Dsl!

FJ40Jim · May 24, 2014

This has been a useful thread. My AC was working fine until this year. Turned on the AC a month ago and no noticeable cooling. Checked pressures w/ gage set, had something like 55 at rest (correct for charged system), 50/60 w/ compressor engaged. Also noted that when compressor engaged, the engine didn't 'load down' at all. The compressor was simply not pumping any useful volume of R134. Searching the forum turns up info on the RCV and its failure mode. A new $20 RCV was ordered from an ebay vendor (may have been a tactical error). When the compressor was opened up, it was spotlessly clean inside. RCV was replaced, system recharged, and exact same result. No compressor pumping. Clutch engages, fans run, but no big pressure differential.

Fine, time to order a new Behr compressor from AutohausAZ. Get the expensive genuine OEM Behr compressor, only to find it is a generic chinese replacement. Oh well, it's bought, hafta install it. Install compressor, evac & charge system.... no AC. What The Frack!
Turns out to have a dead short in the clutch coil, blows the fuse as soon as button is pushed. Now I have to evac the 134, remove new compressor, install old compressor (as a serp belt idler), return new compressor, buy a genuine Japanese Sanden compressor from worldpac.

My small contribution to this thread is:
Do buy the RCV from a reputable vendor with a history of successful sales.
Don't buy a chinese compressor.

thegrinch911 · May 25, 2014

Ok. So one minute cold air. Then the car is idling for 10 mins and no more ac. Checked fans. Drivers side does not come on. But I have the ac light on inside. Compressor does not engage. Does the fan not coming on stop the compressor from engaging? Anyone have this and what did you do to fix it? Thanks much!

csstevej · May 26, 2014

If you do this on the car what are you expected to loose in pag oil when the back of the comp is removed from a normal system?

And what is the danger of too much oil?

What is considered too much?

I suspect my 03 bug is having and rcv issue, need to get gauges and see.

DanG144 · May 27, 2014

You usually lose only a few drops.

Too much oil (in moderation - say 50% too much)will raise the boiling point of your refrigerant, make it run at 40 degrees instead of 36, as an example.

DanG144 · May 27, 2014

thegrinch911 said:
Ok. So one minute cold air. Then the car is idling for 10 mins and no more ac. Checked fans. Drivers side does not come on. But I have the ac light on inside. Compressor does not engage. Does the fan not coming on stop the compressor from engaging? Anyone have this and what did you do to fix it? Thanks much!

http://forums.tdiclub.com/showthread.php?t=242699
You need to go through the diagnostics. It could be several things, one of which is a failing high pressure sensor, which is what I would check first.

thegrinch911 · May 27, 2014

Thanks. I'll check out the link.

snakesausage · May 27, 2014

Thanks to TmpaFL2000Dsl and DanG144 for this thread.

The first time I tried to use my a/c this season it would only blow slightly cool air. I checked the fans, switches, and then hooked up my gauge set and found that the pressures were close to equal. I had a compressor out of my parts car that had a bad clutch and shaft threads so I took it apart and salvaged the valve plate and RCV. After replacing the entire assembly on my car I added about an oz of oil (guesstimate of the amount lost) vacuumed down, leak checked and recharged the system and now it reads 36°F vent temp. I am out a little less than $20 for the oil and refrigerant.

csstevej · May 27, 2014

Thanks Dan.

coronan · Jun 7, 2016

So I read this thread and several others. It looks like the SD7V16 comes in 2 configurations. "Electric" refrigerant control and " analog".
Polarbear does not list a TDI in the parts look up.
Rock auto is all over the place,. Fitting years '99 all the way '09. And different parts for golf, Jetta, and Beatle.
I have an 01 golf tdi.
So how do identify my rcv type???
Attached are some photos.

Here is the less than faithful sticker

Lastly,. I have not found the rcv in exploded diagrams.

DanG144 · Jun 8, 2016

The SD7V16 comes only with mechanical RCVs on it. No electrical in hundreds of MK IV cars that I have seen. Thousands that I have helped folks with on this site. There is no provision for wiring to the INTERNAL RCV on the SD7V16.

The SD7V16 is common to all the gas and diesel models of the Mk IV VW that I have seen.

The MK V cars (2005.5 and later, except 2006 Golf and Beetle) compressors have electrical RCVs.

You can find the proper part numbers for yours, as hundreds have, in the first post of this thread.

atmarine · Jun 16, 2016

Good and timely thread here!
I am just getting to the AC season with our 99 Golf. System has 80 psi when compressor clutch is not engaged. When engaged, about the same with no pressure differential from the discharge to the suction line. The suction gauge does "flutter" slightly when the compressor is running. I am diagnosing this as the refrigerant control valve. I assume it is mechanical not electrical due to the age. Can this be replaced or does the compressor need replacing? Thanks all and especially DanG144 for all the help!

DanG144 · Jun 16, 2016

Is this on a Mk IV? A "99.5" car? I am not sure about the early 99 model. The 99.5 has the SD7V16 with the mechanical RCV inside it.

Are you sure the car has a full refrigerant charge? 80 psi is pretty low. There would have to be a large segment of the system where it was 76 degrees to have pressure that low, and still have a full charge.

It is not impossible but it is unusual to have no differential pressure from a bad RCV, there is usually some differential pressure. The RCV is capable of lowering the displacement of the compressor to 5 cc per revolution, with a max of 160 cc per revolution. Most of the time it can produce some differential pressure.

And I know in NY the whole car might be less than 75 degrees.

If you have enough refrigerant, then you probably have a bad RCV.

atmarine · Jun 17, 2016

Thanks Dan. I was guessing low on charge as well once I saw the clutch engaging. Once I connected gauges I found it very odd that there was no differential pressure. It is indeed a 99.5 / ALH. I also believe it is a SD7V16 compressor as there is no other wiring going to it other than the clutch coil. I can recover the charge and weigh back in the proper charge to confirm that this is not the issue. I would guess the entire car was about 76 degrees as it was in a concrete garage all day on a cooler day in NY. Can the mechanical RCV be replaced if this is the issue?

Would the clutch ever not fully "grab" and cause limited capacity, or no capacity out of the compressor? Thanks again!

DanG144 · Jun 17, 2016

if the clutch is slipping, it creates a lot of heat and then, very soon, noise. They rarely slip.

Yes, your RCV can be replaced and it will probably fix your issues.

coronan · Jun 26, 2016

So I replaced the RCV and drier. Replaced oil in the compressor + 2 oz in the drier. Pulled vacuum on the system for 30 min.
I started loading the system with R134 with the compressor running. I got about 18 oz in then the compressor started cycling with the low side going to ~ 70 psi.

I figured the expansion valve must not be letting any pressure through.
I changed out the expansion valve and loaded less then 12oz in the system when the compressor started cycling again.

This time the pressure was going higher. (90+ psi)

The compressor seems to be making pressure fine. Its not circulating???
Do i need a new compressor or something else?

Thanks in advance!

DanG144 · Jun 27, 2016

1)Is the compressor cycling? clutch turning on and off during operation? This is extremely unusual. It should not happen at all on our systems. Once turned on, the clutch should stay engaged until you turn it off. 2) Was it cycling before you started working on it?

Both of the pressures you have given are what you could expect from a can of refrigerant sitting on a shelf, at ambient temperatures for Reno (about 65 to 90 degrees). What you have not given is the high and low side pressures taken at the same time. We would expect see low side pressures dropping to around 30 psi or so on a good system, even with the expansion valve stuck closed the suction pressures, if anything, would be low.

3) What are your fans doing? a)Are they cycling speeds? b)Both running together at matching speeds?

4)Did you drain out the old oil first? a)Completely empty the compressor? 5)How did the oil look? 6)How much total oil did you add? Normally when replacing the RCV and drier, at most you will need to add one ounce of oil to the system.

Lots of questions, and the answers are pertinent to finding the solution.

coronan · Jun 27, 2016

Thanks Dan!

1) Compressor Cycling:
Compressor ran at first then starts cycling. I dumped in about 8 oz into the high side. Then started the car. Compressor ran. Then I Started slowly adding to the low side to suck in the remainder of the 12 oz can. Compressor started cycling. Spiking to 90 psi on the Low side. High side never went higher than low side. (restriction?)

2) Original problem: The ac ran for a 2 weeks this summer then started cycling. Due to the cut out pressure switch doing what its supposed to do. Cuts out at ~60+ psi.
Hi side never goes higher than the low side pressure. I found this thread and changed the RCV. Then the Expansion Valve.

3) I was not watching the fans. I'm pretty sure i smoked the clutch yesterday. Low side went to 130 psi. High side stayed at 90 psi. Then i smelt hot electrical and shut it down.

4) I drained the compressor completely on the bench.
5) Oil looked good. Yellow with a hint of silver.
6) I read Sanden literature that the system should get 4 oz. Compressor bottom end held 2 oz. I put the rest in the drier.

What would the low side to go higher than the high side?

DanG144 · Jun 27, 2016

Do you think that you burned something up?
The pressure SENSOR (it is not a switch, no matter what nomenclature VW uses - and it will be damaged it you try to bypass it) is supposed to shut off the compressor clutch at +450 psi on the high side. The clutch on this AC system should NEVER shutoff once started. If it does, something is badly wrong.
As long as the hint of silver in the oil was not from metal flakes, the oil sounds good.
The RCV should try to control the low side pressure to 30 psi or so. It should start out about 100 from the ambient temperature car, then go down to about 30 and stay there.
You need to watch the fans it is very important to know what they do. Try the key on AC on, engine off test, verify they both work in slow speed. You are working on your 01 Golf, right?
The low side will go higher than the high side (momentarily) if you have a sun heated cabin and turn on the cabin fan, the cabin must be hotter than the condenser coils, if the compressor is not functioning. This is a very unusual short term condition that almost never exists.
You are positive that the compressor clutch was engaging and turning the compressor? You should be able to turn your compressor center shaft easily with light finger pressure when the car is off. Check this.
Watch to ensure the clutch actually engages and starts turning the face of the compressor clutch and center shaft.
I suspect that you may have a problem with your high side schrader valve, that it is not opening, when your gauges are hooked to it. Please verify that your high side can start at zero (bleed off your gauge high and low side to zero) then goes up when you hook on only the high side. Try to verify your manifold gauge cross connect valves are closing properly. When taking readings both valves should be closed, forgive me if already know this.
One common failure mode for the high pressure sensor is for the signal out to ramp from low to high pressure (with the input constant). This shuts off your compressor when the signal reaches 450 psi equivalent. Then it turns the compressor back on as the signal ramps down.
You can verify this signal with a duty cycle meter.
The failure of the HP sensor (which VW parts does call a switch) will not cause all of your symptoms.

DanG144 · Jun 27, 2016

Why does the Advanced post editor insist on removing the lines between paragraphs, or the ones I put in to make the post easier to read. This is REALLY aggravating.

DanG144 · Jun 27, 2016

coronan,
I really think that you are having problems with the schrader valves and gauge couplings. This is very common on the VW.

coronan · Jun 27, 2016

What is the solution to the schrader valves????

whitedog · Jun 27, 2016

DanG144 said:
Why does the Advanced post editor insist on removing the lines between paragraphs, or the ones I put in to make the post easier to read. This is REALLY aggravating.

Chrome does it, IE doesn't. If I edit a post in the no start thread, I use IE so I don't lose the spacing.

volmaniac · Jun 27, 2016

DanG144 said:
Do you think that you burned something up?
.
The pressure SENSOR (it is not a switch, no matter what nomenclature VW uses - and it will be damaged it you try to bypass it) is supposed to shut off the compressor clutch at +450 psi on the high side. The clutch on this AC system should NEVER shutoff once started. If it does, something is badly wrong.
.
As long as the hint of silver in the oil was not from metal flakes, the oil sounds good.
.
The RCV should try to control the low side pressure to 30 psi or so. It should start out about 100 from the ambient temperature car, then go down to about 30 and stay there.
.
You need to watch the fans it is very important to know what they do. Try the key on AC on, engine off test, verify they both work in slow speed. You are working on your 01 Golf, right?
.
The low side will go higher than the high side (momentarily) if you have a sun heated cabin and turn on the cabin fan, the cabin must be hotter than the condenser coils, if the compressor is not functioning. This is a very unusual short term condition that almost never exists.
.
You are positive that the compressor clutch was engaging and turning the compressor? You should be able to turn your compressor center shaft easily with light finger pressure when the car is off. Check this.
Watch to ensure the clutch actually engages and starts turning the face of the compressor clutch and center shaft.
.
I suspect that you may have a problem with your high side schrader valve, that it is not opening, when your gauges are hooked to it. Please verify that your high side can start at zero (bleed off your gauge high and low side to zero) then goes up when you hook on only the high side. Try to verify your manifold gauge cross connect valves are closing properly. When taking readings both valves should be closed, forgive me if already know this.
.
One common failure mode for the high pressure sensor is for the signal out to ramp from low to high pressure (with the input constant). This shuts off your compressor when the signal reaches 450 psi equivalent. Then it turns the compressor back on as the signal ramps down.
.
You can verify this signal with a duty cycle meter.
.
The failure of the HP sensor (which VW parts does call a switch) will not cause all of your symptoms.

readability dots.

DanG144 · Jun 28, 2016

Volmaniac,
Thanks for the tip. It looks as if SAFARI browser eliminates the spaces as well.
Dan

DanG144 · Jun 28, 2016

The best I have done with the Schrader valves was to buy a set of gauges with adjustable depth on the connectors. Then try different depths until it works. Too shallow and it won't open, too deep and it blocks it off again.

Then sometimes, all you can do is replace the fixture, and try again. Remember on our systems the whole fixture unscrews.

coronan · Jun 28, 2016

I spoke with Polarbear inc again. They said the clutch is not toast until it get so hot that the black paint turns white. Also the coil should test good between 3 - 5 ohms.

They also said the compressors can do funny things if they are not fully charged.

Today I finished loading as much of 2 12 oz cans as I could with the engine off (per polar bears recommendation)

Testing:

Key on, Engine off, AC on = No fans spin

Engine running (cold), AC on, Compressor spinning (first minute). = No fans spin.

2nd minute = compressor starts cycling, Drivers side fan spins slow. low side 65 - 75 psi.

atmarine · Jun 28, 2016

RCV question

When you folks are replacing the RCV on the Sanden compressors, are you doing this in the car or out of the car? Thanks!

A/C Fix You May NOt Need A New Compressor

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