Question about the compressor cycle time

[mburshtain]

Hi Guys,
What should be a normal cycle time for the A/C compressor? my car is blowing cold air, but the compressor re-cycle every 5-8 sec.
Due to that quick cycles, my fan relay is getting really hot.
I know that normally it could mean that I'm low on refrigerant, but I was wondering if there is any way to Troubleshoot before adding more R12.

[Bitsyncmaster]

With a gauge set on the system you can usually tell if your low on charge by seeing lower than normal high pressure side. The low pressure side is controlled by the low pressure switch so it always runs about 20 to 40 PSI.

The high pressure is dependent on ambient air temp, and the amount of air the cooling fans are drawing.

Since your still running R12, my guess is you are low on the charge. If it had been converted often the problem is contamination of the system which plugs up the orifice and condenser.

[David T]

If the low pressure switch has not been adjusted, you probably need a small amount (less than 16 oz) of R-12. Of course that also depends on the ambient temperature that you were testing at. If it was very hot you are definitely low.

[mburshtain]

My A/C is still on R-12 and my low pressure switch was never adjusted.
I will check the low and high reading tomorrow.

BTW, can anyone direct me to the spec showing what should be the correct pressure?


Sent from my iPhone using Tapatalk

[mburshtain]

My A/C is still on R-12 and my low pressure switch was never adjusted.
I will check the low and high reading tomorrow.

BTW, can anyone direct me to the spec showing what should be the correct pressure?


Sent from my iPhone using Tapatalk

That's the one, right?

50479

[cdrusn]

As a rule of thumb psi of 35 on the low side should be accurate enough. If it's cycling it's the low pressure switch protecting the compressor. Why not convert to R134 while you're at it? It really is hard to over fill but at 35 psi it's at it's top end. :race:

[Bitsyncmaster]

That's the one, right?

50479

Yes that should give you a reference of what to expect. What makes if cycle faster is the low side pulls down faster because there is not enough liquid Freon feeding the orifice.

[mburshtain]

It might be a trivial question, but I had to ask.
I should measure the pressure, on both high and low side while the A/C is running, right? the important thing would be to capture the PSI on before the compressor clutch is engaged and once it is disengaged. Correct?

[Bitsyncmaster]

It might be a trivial question, but I had to ask.
I should measure the pressure, on both high and low side while the A/C is running, right? the important thing would be to capture the PSI on before the compressor clutch is engaged and once it is disengaged. Correct?

Static pressure only shows you if your system has some charge. You can find the static pressure via a temperature table of R12. As long as you have any liquid Freon, that pressure is accurate.

You want to look at both sides. If you see the low pressure going to low that would indicate a bad low pressure switch (I found one on a friends car). The high side is where you can get more data to determine what is wrong.

[mburshtain]

Here is what I see in my static reading at 55 degrees. Both the high and low side of the system have equalized.
Could it be that on my last service they overcharged my AC?
https://uploads.tapatalk-cdn.com/20170403/b2e87847d55844aebde2580f645b54f9.jpg


According to this table (http://i.imgur.com/7tk1qr3.jpg), I should expect to see around 52 PSI at 55 degrees.

[Bitsyncmaster]

Here is what I see in my static reading at 55 degrees. Both the high and low side of the system have equalized.
Could it be that on my last service they overcharged my AC?
https://uploads.tapatalk-cdn.com/20170403/b2e87847d55844aebde2580f645b54f9.jpg


According to this table (http://i.imgur.com/7tk1qr3.jpg), I should expect to see around 52 PSI at 55 degrees.

The temperature would have to be what the system is at. If your air temp has been constant for a few hours and the engine is cold then the air temp should be close to what the system temp is. You would see the same pressure even with a system under charged or overcharged. (a few oz to 5 lbs of R12).

Note the middle red scale (R12 scale) that shows your system must be at 60 deg. F. The gauge accuracy is not perfect so your pretty close. Yes both sides should read the same after the system has bee off a while.

[mburshtain]

Thanks for all your help so far.
Here is a short video showing my readings when the AC is on, fan is set to 1.

http://www.youtube.com/watch?v=aQ6_JpOao84


PSI on the low is between 23 to 44 and on the high between 70 to 123

Sent from my iPhone using Tapatalk

[Bitsyncmaster]

Thanks for all your help so far.
Here is a short video showing my readings when the AC is on, fan is set to 1.

http://www.youtube.com/watch?v=aQ6_JpOao84


PSI on the low is between 23 to 44 and on the high between 70 to 123

Sent from my iPhone using Tapatalk

Normally you test with the fan on MAX speed, doors open and set to NORM AC. Also good to also see with your engine RPM higher (quick test to read high pressure). But from what I see, your low on R12.

[mburshtain]

Normally you test with the fan on MAX speed, doors open and set to NORM AC. Also good to also see with your engine RPM higher (quick test to read high pressure). But from what I see, your low on R12.

Thank you Dave.
My rpm is between 900 to 1100 while the AC is on.
I run the same test again as you suggested with both doors open and AC is set to max.
Now I'm getting:
Low - 23 to 45
High - 90 to 140

EDIT - after letting it run a while (10 min), it is stabled at 26 PSI on the low, and 145 and the high. No quick cycles while the doors are open.


Sent from my iPhone using Tapatalk

[Bitsyncmaster]

Thank you Dave.
My rpm is between 900 to 1100 while the AC is on.
I run the same test again as you suggested with both doors open and AC is set to max.
Now I'm getting:
Low - 23 to 45
High - 90 to 140


Sent from my iPhone using Tapatalk

I don't do much testing when the air temp is cold. You should use your chart to compare what pressures your getting at the ambient air temp. R12 runs lower high side pressures. I run R134a so I normally top off AC on a hot day by reading the center vent (fan on speed 4) to get maximum cooling but watching the high side pressure to not exceed the charts.

The best way to charge is evacuate and use the correct weight of the charge. But you can't do that just topping off.

You probably don't have a 30 lb. tank of R12 to just try a little more charge to see if your cycle get longer.

By the way, if you run my Fan Relay, It will keep the fans running even with a short AC cycle. My fan relay extends the fan run times by 20 seconds. I did that to improve the AC and not cause the idle and electrical noise from the fans turning on and off. Each OEM fan has a starting current of 48 amps and quickly drops to normal.

[mburshtain]

I think you're right and I will need to flush it all and start clean. Unfortunately, I only have 12 oz cans so I will need 3 cans + 1/3 to reach 2.5 pounds of gas.
Sounds about right?
What type of available oil should I add after flushing the system?
Do you think it worth adding 12 oz to check if the cycles are decreasing?


Sent from my iPhone using Tapatalk

[Bitsyncmaster]

I think you're right and I will need to flush it all and start clean. Unfortunately, I only have 12 oz cans so I will need 3 cans + 1/3 to reach 2.5 pounds of gas.
Sounds about right?
What type of available oil should I add after flushing the system?
Do you think it worth adding 12 oz to check if the cycles are decreasing?


Sent from my iPhone using Tapatalk

If it was me, I would add the can but watch your high pressure. With R134 on a hot day the high pressure runs about 250 PSI or more. I think R12 runs about 200 PSI on a hot day.

Adding the can now will tell you if you have a leak by it returning to the quick cycle again later. Better to loose that one can of R12 than a full charge.

[mburshtain]

Smart advice, I will give it a try. I will also add some AC dye


Sent from my iPhone using Tapatalk

[Ron]

Unfortunately, I only have 12 oz cans so I will need 3 cans + 1/3 to reach 2.5 pounds of gas.
Sounds about right?
No -- 3 and 1/2 cans is 3.5 x 12 = 42 oz, or 2.625 lbs.

Anywho, Service Bulletin ST-29-11.81 changed the R12 charge to 2.2 lbs:
2.2 lbs = 35.2 oz, or 2.93 12 oz cans.

[mburshtain]

Thank you Ron


Sent from my iPhone using Tapatalk

[mburshtain]

A quick update- I installed Bitsyncmaster's Electronic Fused Fan Fail relay and the Solid State Fan relay. Now I'm not seeing the quick cycles of the fan. No more unnecessary relays overheating. This is an amazing product.
As soon as I get a chance I'll also recharge my A/C, it's still blowing cold, so no rush.


Sent from my iPhone using Tapatalk