Dash AC woes on my 345

[Air345Fly]

My dash AC was not working and the PO said that it has not worked
for a long time. It had been converted to R-134A.

The original R-12 capacity was 3 LBS 8 OZ according to these two
manuals:
http://www.73-87chevytrucks.com/tech...ice_Manual.pdf
on page 84.
and this manual;
http://www.73-87chevytrucks.com/tech...ice_Manual.pdf
on page 71.

I have a Sanden compressor and the Sanden manual here:
http://www.erareplicas.com/gtman/ac/sanden.pdf
recommends 95% reduction in charge for R-134A on page 32.
That is 3 LBS 5.2 OZ.

I have seen elsewhere a reduction to 70% which is 2 LBS 7.2 OZ.

I have the original ARA evaporator unit. Everything seems to be
in good condition for it's age.

I replaced the receiver and pulled down a vacuum for over an hour.
I let it sit overnight with a vacuum and it held OK. Pulled the
vacuum again for an hour before charging.

Now comes time to charge it. I put 2 12 OZ cans in it without
running the engine. That is 1 LBS 8 OZ. The pressure was over
50 PSI. I started the engine and turned on the AC. The compressor
came on. It started to cycle on the temperature bulb in the evaporator.
The evaporator coil got cold. It is not very warm today, about 65 degrees.

I started to add a third 12 OZ can, can upright, vapor only, and the
compressor would make a horrible noise for a few seconds then start
to turn normally and then make no noise.

It seems that I am slugging the compressor. I was keeping the can
upright so that should not have caused the slugging. Have I added
too much R-134A even though I am way below the amount that I
think that I need?

I have read most of the discussions on this forum but no one seems
to say how much R-134A is needed.

Thanks,
Pete.

[mehes]

Pete, did you also add the proper amount and type of oil?

[vswingfield]

Originally Posted by Air345Fly

...

Have I added too much R-134A even though I am way below the amount that I think that I need?

I have read most of the discussions on this forum but no one seems to say how much R-134A is needed.

Thanks,
Pete.

Unfortunately charging Air-conditioning systems isn't like changing oil. Just pouring in x amount will not give you the correct pressures in the system. Even back in the R12 days, the proper charge varied from the published "correct amount."

Proper system charging is determined by observing the pressures on the low side and high side of the system using your set of AC manifold gauges. (Link to Amazon for example)

Having said that, what are the low side and high side pressures you have observed?

Interestingly, overcharging the system will keep it from cooling properly. I have seen (in the old days) an R12 system charged till it has 95 psi on the low side and wouldn't cool properly. (With R12, the low side psi reading correlates closely to the degrees Fahrenheit that the system cools to. Gross oversimplification of the refrigeration cycle, but keeping it short here.) This system was actually cooling, but only down to 95 degrees. Removing coolant until the low side pressures dropped to the mid 30s resulting in ice-cold air coming out from the dash.

You really need to use a set of gauges to know what's going on.

[Air345Fly]

Originally Posted by mehes

Pete, did you also add the proper amount and type of oil?

I put 2 OZ of PAG 100 oil into the receiver before I installed it.
I got the "2 OZ" value from a list of components and their oil
usage or coating needs.

Pete.

[Air345Fly]

Originally Posted by vswingfield

Unfortunately charging Air-conditioning systems isn't like changing oil. Just pouring in x amount will not give you the correct pressures in the system. Even back in the R12 days, the proper charge varied from the published "correct amount."

Having said that, what are the low side and high side pressures you have observed?

You really need to use a set of gauges to know what's going on.

I do have a set of gauges but I stopped the charging process when
I started slugging the compressor. I figured that I needed to ponder
and ask some questions.

Before the slugging I seem to remember the low side pressure at
about 0 PSI. I was not paying too much attention after that because
I thought that I has a ways to go before the system was nearing
full.

Pete.

[vswingfield]

Sounds like you're on the right track.

You did put oil in, so we don't have to worry about that. Did you evacuate the system. I'm assuming that you did.

At the risk of oversimplification again; I usually pay more attention to the low side than the high, myself. Do you recall what the high side pressures were, though?

Since the noise stops and it seems to run normally, I probably would try adding some more, slowly like your were doing. Can upright, vapor only. Maybe only slightly crack the valve and let it trickle in. See if you can get the low side up to the mid 30s or so without the high side going through the roof.

Let us know how things work out.

[Air345Fly]

After sitting all night I was out there again. Before starting the engine
I measured the pressure at 52 PSI. Running the system the compressor
cycled without slugging. Everything sounded OK. The low side pressure
was about 9 PSI and the high side was at 91 PSI. It is about 60 degrees
outside. The pressure at rest was higher yesterday but the outside
temperature was also higher.

More work to do!

Pete.

[vswingfield]

Did you try adding more coolant once you started it?

[Keyair]

I have this in my future, so great post, with great links!

You pretty much did what I have done in the past, when recharging. I too pull a vac, which removes moisture, any remnants of old stuff and leak checks.

I normally then run the AC, with the engine idling at 1800rpm and check what the temps are at the vents vs ambient, whilst watching the pressures.

When I did my 1990 Mercedes 190 2.6, I replaced the O rings in the whole system, then recharged with R12. I dont remember how much it took, but I can tell you looking at the pictures I have that with the ambient temp at 86deg and the engine running at 2000 rpm my low side was 30psi, high side was 140psi, and I was getting 35 deg out of the center vents.

Also, make sure your AC triggers the Condenser fan to run.

Update us!

[Air345Fly]

I was away for a few days but got back at it today.

I measured the pressure with everything cold, about 60 PSI.
I ran the engine and measured the high side at 100 PSI.
I could not measure the low side because I don't have a means
of connecting the can of R134a to my gauge setup. I can only
connect the can directly to the low side.

At the ambient temperature of 68F the high should be 145 to 160 PSI
according to the charts.

Since the high side was low I added some more R134a vapor.
Everything was going OK, the A/C cycling normally. When I hit
105 PSI on the high side the compressor started slugging.
I stopped everything.

Now I am really confused. Do I have too much freon even though
my pressures are low? Could I have too much oil?

My system has the sight glass, can I learn anything from that?

Pete.

[Air345Fly]

Well, back at it.

I figured that if the compressor is slugging that there must be too much
freon. At the start I am getting 8 PSI low side and 100 PSI on the high
side and the compressor is slugging. The outside temperature is 65F.

I let freon out until I got -1 PSI and 90 PSI with the compressor still
slugging! What could that possibly be? Could I have too much oil?

The system is still producing cold but I don't run it long enough to
try to get to 40F out of the vents.

Pete.

[vswingfield]

Could you explain "slugging"? I'm not sure what i assume you mean is really what you intend.

[mehes]

If you are not sure of the condition of the system when you started (PO says hasn't worked for a few years) and the problems you are seeing now, it Might be time to go back to square one. Evacuate the system. Physically remove the compressor and drain out the oil. Get a new receiver/dryer. Blow out the coils and lines as best you could and start putting things back together. You might also consider replacing the thermostatic expansion valve at this point. Just a suggestion. Who knows what is in there now.

[Air345Fly]

By slugging I mean that the compressor makes a terrible noise for some
seconds when the clutch engages. After the few seconds the compressor
begins to turns quietly and produces cooling. While slugging the belt
appears to be slipping as it seems to loosen on one side and hump
over the pulley. The belt is properly tensioned.

After I put the first 12 OZ can in the system the compressor cycled
normally. Since I was way away from the 3 LBS + that the system
should take I did not measure the pressures. When I started adding
the second 12 OZ can it began slugging. When I measure the pressures
they are low.

[Air345Fly]

Originally Posted by mehes

If you are not sure of the condition of the system when you started (PO says hasn't worked for a few years) and the problems you are seeing now, it Might be time to go back to square one. Evacuate the system. Physically remove the compressor and drain out the oil. Get a new receiver/dryer. Blow out the coils and lines as best you could and start putting things back together. You might also consider replacing the thermostatic expansion valve at this point. Just a suggestion. Who knows what is in there now.

I am beginning to think that you may be right.

Pete.

[vswingfield]

Originally Posted by Air345Fly

I am beginning to think that you may be right.

Pete.

I agree. Get everything out, clean relentlessly, and start fresh.

You've asked in previous posts if there could be too much oil, that's a distinct possibility. Excess oil could pool in places (like a capillary tube) causing a hydraulic lock until some seeps through creating the slugging sensation.

Other impurities, such as desiccant that have escaped from the receiver/dryer can also plug small orifices. Happened to me once in my 1973 GMC pickup. What a mess to clean up.

Best of luck. I've been hoping that someone would have a solution that was less work, but it sounds like it's time to do the hard stuff.

Keep us informed. We're pulling for you.

[John Woodrow]

Compressors can make weird noises if unused for a long time. I had an old Ford truck that I resurected the A/C system on. The compressor seriously sounded like it was going to throw a rod for a while but did settle down and work fine.

[Air345Fly]

Continuing my dash A/C saga, I opened up everything and flushed all the
cores and hoses out with cleaning fluid. I flushed everything into a clean
paint can using a paper towel to capture any junk that might have come
out. Everything was clean and no evidence of any junk in the towels.

I replaced all O rings with the new green type. I put a new receiver in
the system. I put 2 OZ of oil in the receiver. I put 4 OZ of PAG 100 oil
in the compressor after dumping the old oil out.

I pumped a vacuum and let it sit for a week. The vacuum held OK.

The quick connectors that I used last time leaked when I used them
this time so I bought a different type which worked OK.

This time I was going to use the temperature and pressure measurements
to determine when I had put enough freon in the system. I got a cheap
dual thermocouple meter off eBay for the temperature measurements.

I connected one thermocouple to the exit pipe of the evaporator core
and the other thermocouple to the suction pipe at the compressor.
I wanted to see if there was any temperature difference. DIDN'T
WORK! The meter must be sensitive to small voltage differences
between the evaporator and the compressor. If I disconnected
one thermocouple it worked OK. The two inputs must not be
isolated.

I ended up adding 2 12 OZ cans of freon and perhaps a quarter of
another. There is no slugging and the system is cooling but the
compressor does not sound right. I think that I might have added
too much. The final readings were 150 PSI high side and 14 PSI
on the low side. The suction side temperature was 43 degrees F.
The outside temperature was 65F.

The low side pressure was too low at 14, it should be 25 to 35 PSI
according to the chart. The high side is OK. The suction side
temperature was OK at 43F.

I don't have a lot of confidence in my results. The pressures
would change a lot depending on the engine RPM but I guess that
is to be expected. The compressor would cycle every 10 seconds
or so thus the pressure and temperature did not really stabilize.

Also I have the cover off of the evaporator/heater box. This results
in little air flow through the core. Probably the cause of the rapid
compressor on/off cycling.

I think that it is too cold to complete the job with confidence and will
wait to the spring.

Pete.

[Air345Fly]

Today was warm around here so I thought I would give the dash A/C
a try. I did not connect any gauges. I did finish assembling the
heater / A/C box that is in front of the passenger seat. This will
cause the fan to draw air through the evaporator core.

It seemed to work OK. The A/C compressor did not cycle but ran
continuously which I believe is the way it should work. The air
temperature coming out of the vents was about 42 degrees F.

I think that the A/C job might be done!

However after running a while the belt started slipping, I might
have had it too loose. Might need a new belt.

Pete.

[Keyair]

Awesome! Keep us updated!