Automotive Air Conditioning Information Forum (Archives)

dalemarek on Mon June 30, 2014 6:10 PM

Year: 1979
Make: VW
Model: Super Beetle
Engine Size: 1600
Refrigerant Type: R12
Ambient Temp: 70
Pressure Low: Unk
Pressure High: Unk
Country of Origin: United States

Beetle has an aftermarket dealer installed VWCOOL AC system. Had it charged and everything worked well on low and high fan speed. When I switched to highspeed the fans stop after a short time. Cycling the fan switch after a short rest returned the power. First replaced the fan switch and power connector which were a bit charred at the incoming power. Same issue so I replaced the AC relay feeding the 3 speed switch. All works normally when the engine is off. Start the car - low and medium speed no issues, switch to high and the circuit breaker at the battery terminal cuts the power. Current draw with low fan about 5.7A and going to high pulls about 7.9A measured at the battery with the engine off. Maybe close to 9A with the engine on and the clutch engaged. I did notice that with the meter in series the fans do not get full speed and the meter gets quite hot. This is only while the engine is running. Everything seems to engage and turn freely at the compressor but I suspect the issue may have to do with the clutch. Does any of this sound familiar? Just trying to narrow it down before I take it back to the shop. Just seems odd that it get the meter so hot but it is close to its limit of 10A. I know this is an old system so I do not have much information. What do yo u think?

mk378 on Mon June 30, 2014 6:15 PM

The interior fan motor may be bad.

If the clutch is also on the same circuit breaker, check that the clutch doesn't draw more than 4A. Or test with the compressor wire disconnected so only the fan runs.

dalemarek on Mon June 30, 2014 6:23 PM

Will measure the current draw for the clutch. I only see one black wire going to it (is it grounded thru its housing?) With the clutch not engaged or the engine not running there doesnt seem to be enough current to trip the circuit breaker. Maybe I am measuring in the wrong place (at the battery) but the current draw does not approach the 40A rating of the breaker.

mk378 on Mon June 30, 2014 11:15 PM

A single-wire clutch would indeed be grounded through the frame.

Circuit breaker may be worn out and tripping at less than 40A, but the burnt wiring suggests there is indeed an over-current.

There are clamp-on ampmeters which can measure DC current without breaking into the circuit.

bohica2xo on Tue July 01, 2014 11:16 AM

Meters are test instruments, and many of them barely support 10 amp current testing. For that sort of thing you need a shunt. The test leads & banana plugs on a meter are really only good for about 2 amps.

Your problem is most likely a bad thermal circuit breaker. A 30+ year old 2 dollar part. Set your meter to volts. Ground the negative test lead at the battery post. Key on, engine off, A/C on. Check the voltage drop from the positive battery post to the input of the circuit breaker, then check the output of the circuit breaker. If you see more than a 0.1v drop across a 40a breaker it is time to replace it.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

wptski on Tue July 01, 2014 2:52 PM

Quote
Originally posted by: bohica2xo
Meters are test instruments, and many of them barely support 10 amp current testing. For that sort of thing you need a shunt. The test leads & banana plugs on a meter are really only good for about 2 amps.

Your problem is most likely a bad thermal circuit breaker. A 30+ year old 2 dollar part. Set your meter to volts. Ground the negative test lead at the battery post. Key on, engine off, A/C on. Check the voltage drop from the positive battery post to the input of the circuit breaker, then check the output of the circuit breaker. If you see more than a 0.1v drop across a 40a breaker it is time to replace it.
I have the A Series.

dalemarek on Wed July 02, 2014 4:35 PM

Okay a quick update. Thank everyone for their input. It is a valuable learning expierence. So I could not find my clamp on AMP adapter for the volt meter but I did get a new thermal curcuit breaker. Took a chance and hooked everything back and the system ran for a good 5 minutes on high at engine idle without tripping anything. Before, I could not get more than 10 or 20 seconds. The batery connection stays room temperature but the relay that powers the fan switch, condensor fan and compressor clutch gets a little warm to the touch. About 20 degrees F above room temperature at 82F. So a quick question from a newbie.

The suction connection going into the compressor is cold to the touch and sweats a little. The discharge connection is dry and hot as is the top of the upright compressor. Is it normal for the compressor to get hot (about 112F with an outside airtemp at 80F)? Hot air is being discharged up front on the Super Beetle where the have a fan to help cool what I imaging is the condensor.

Sorry, I know it is a basic question but I am an Xray Technologist just learning about this stuff. Humor me. People are so much easier to understand

bohica2xo on Thu July 03, 2014 3:19 PM

The relay coil generates a little heat. If the relay is as old as that breaker was, it may have developed some contact resistance as well. I would replace it when I had a chance.

The compressor will get warm. When the system is properly charged I would avoid touching it to see just how warm it can get... The oil sump below the shaft can reach 180F in some cases.

You have described a York type compressor. Common on air cooled VW installations.

The suction line may sweat all the way to the compressor in some cases. If you can locate the receiver / dryer, it should have a sight glass on top of it. With the system running, observe the sight glass - is it foam? A few bubbles? Clear?

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

dalemarek on Thu July 03, 2014 5:03 PM

Thank you for the reply. I will see if I can access the dryer. On the Bug it is up under the wheel well so it may take some doing. I was using an infrared spot thermometer to test the temperatures but thanks for the warning. On the Bug everything is hot so I have learned. I bought a clamp on multi meter to check the current again. It has three scales 20~ and 200~ 400~ The manual only talks about measuring AC current (will this work on DC) I clamped it to the positive wire just after the circuit breaker and it does read (but it is showing 0.06A at low fan, 0.08 and 0.19 med and full speed, engine off) So on 20~ does that sound correct or too low. It bumps up a couple more points with the engine running and compressor on and air cooling. Otherwise I think I am going to drive it around and see how things go before I put all the covers on. The relay that was warm is also new.

dalemarek on Thu July 03, 2014 5:16 PM

Correction the reading was different with the wire centered in the clamp . 0.12A, 0.21A and 0.40 for high fan.

wptski on Thu July 03, 2014 7:18 PM

Quote
Originally posted by: dalemarek
Correction the reading was different with the wire centered in the clamp . 0.12A, 0.21A and 0.40 for high fan.
I believe that you don't have the correct meter as the current looks a bit low for a fan to but I've never measured one before. The meter would be plainly marked AC and DC on the selector switch. Here's a

Extech that I've owned for years.

Edited: Thu July 03, 2014 at 7:23 PM by wptski

mk378 on Thu July 03, 2014 8:47 PM

The older / less expensive clamp on meters can ONLY measure AC. What it seems you are looking at is "ripple" current caused by the motor not drawing a constant current as it rotates. This is essentially a small amount of AC on top of a large DC current that the transformer in the meter cannot respond to.

You need a meter designed for DC. They are based on a Hall effect device (instead of a transformer) to be able to measure DC.

This one seems to be a cheesy no-name, but there are several choices in the $100 price range. I've used a Greenlee but I don't remember what the model number was.

http://www.amazon.com/UT204-True-RMS-Auto-ranging-Clamp-Meter/dp/B005G4VKFY/ref=sr_1_15?s=hi&ie=UTF8&qid=1404435457&sr=1-15&keywords=DC+clamp+on+meter#productDescription

Edited: Thu July 03, 2014 at 9:01 PM by mk378

bohica2xo on Thu July 03, 2014 9:09 PM

Most clamp meters are for AC, as already stated. DC clamps are usually much more expensive than the simple AC unit.

If the dryer is under the fender, you will need a mirror & a flashlight. Clean the window on top of the dryer. Sometimes an inline sight glass has been installed someplace easier to access - if you have one it will be between the dryer, and the expansion valve.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

dalemarek on Mon July 07, 2014 7:52 PM

Okay then - thanks for the meter lesson. I have alot to learn.