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A/C Compressor Short Cycling?

Tiny
CANNON1349
  • MECHANIC
  • 1997 FORD TAURUS
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 182,000 MILES
The car has a compressor that is 5 years old, and brand-new condenser and all new lines. The evaporator is original. Pressures are normal except the high side climbs up until the switch kicks it off and it will short cycle 3 or 4 times until it runs for 2 minutes and then it will short cycle again. After 30 minutes of running, the compressor does not short cycle and pressure on the high side rests around 250 psi, and the air temperature is good, and everything works normally. I'm starting to think it may be an engine performance or throttle issue. Seems like when the fan turns on, the rpms drop to 600 and the compressor turns off, jumping the rpms to 800 and then it turns on. By the 4th time, the compressor stays on around 650 rpm. Normal idle with the compressor running is about 800 rpm. Also, if I rev the engine the rpms will return down to 600 where the compressor will shut off, and I can effectively make this scenario happen whenever I want.

I'm thinking there may be too much oil in the system, or a weak fan motor, what do you guys think?
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Wednesday, May 24th, 2023 AT 9:48 AM

18 Replies

Tiny
CANNON1349
  • MECHANIC
  • 670 POSTS
I'm starting to think it may be an engine performance or throttle issue. Seems like when the fan turns on, the rpms drop to 600 and the compressor turns off, jumping the rpms to 800 and then it turns on. By the 4th time, the compressor stays on around 650 rpm. Normal idle with the compressor running is about 800 rpm. Also, if I rev the engine the rpms will return down to 600 where the compressor will shut off, and I can effectively make this scenario happen whenever I want.
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Wednesday, May 24th, 2023 AT 3:16 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
This sounds like too much oil is the system or the compressor is starting to come apart and the seals are starting to plug up the orifice tube. I would vacuum the system down and open it up to check the oil and other contaminants. The seals will cause little grey pieces.

Here is a guide that will help:

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

Please go over this guide and get back to us.
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Thursday, May 25th, 2023 AT 9:10 AM
Tiny
CANNON1349
  • MECHANIC
  • 670 POSTS
The issue was happening before replacing all of the lines and new condenser. The evaporator was flushed. And the cycling switches are new. So, the chances are leaning towards too much oil or a problem with the fan. There is a noticeable drop in rpm when the fan turns on. What are the specs for checking the fans on this car? There are two fans, with two separate connectors.
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Thursday, May 25th, 2023 AT 9:25 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

I noticed it has been three days since we have made contact. Have you been able to make any progress?

Let us know.

Joe
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Sunday, May 28th, 2023 AT 7:09 PM
Tiny
CANNON1349
  • MECHANIC
  • 670 POSTS
I've still narrowed it down to either too much oil or a problem with the cooling fans. Again I noticed that the cooling fans put a load on the engine causing a drop in rpm, and it seems like every time the rpm drops to 600 the compressor will shut off and short cycle, and I can replicate this by revving the engine and letting the RPMs bounce back to idle speed, each time bottoming at 600 rpm and causing the compressor to short cycle.

So, I am curious as to what voltage or resistance I am looking for to test the fans and/or connectors going to them. There are two and they are separate.
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Sunday, May 28th, 2023 AT 7:28 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
When the A/C is engaged, the condenser fan turns on. The load you feel is likely either the compressor's load or I guess it could be the fans, but that would be unlikely. If the fans are drawing too much amperage, it will cause a fuse to fail.

The correct idle speed should be between 760 and 850. The idea that it drops to 600 may be caused by the idle air control valve (IAC). The IAC is responsible for maintaining idle speed and is controlled by the PCM. When the added load of the compressor is placed on the engine, the IAC should adapt and maintain 760 to 850.

The IAC is mounted to the throttle body (see pic below). You may want to remove it and inspect where it attaches to make sure there isn't any carbon or dirt restricting airflow. If there is, here is a link explaining how to service it.

https://www.2carpros.com/articles/idle-air-control-valve-service

Let me know your thoughts.

Take care,

Joe

See pic below
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Sunday, May 28th, 2023 AT 8:43 PM
Tiny
CANNON1349
  • MECHANIC
  • 670 POSTS
The idle does drop to 600, or at least just above the 500 RPM mark. It's interesting to think it may be the IAC valve, because if I hold the gas where the car is staying at 800 RPMs or so, the compressor will never short cycle, and I've tested this by leaving my foot there for 30 minutes. I'll inspect this and see how it does.
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Monday, May 29th, 2023 AT 9:33 AM
Tiny
CANNON1349
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Well, I cleaned the valve, and yes it was dirty, but it changed nothing. I still think it is significant that the fans cause a drop in RPM. Any other ideas?
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Monday, May 29th, 2023 AT 11:53 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,665 POSTS
Even though the valve was dirty it could be not working as well, I would try a new valve to see if that fixes it.
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Tuesday, May 30th, 2023 AT 9:30 AM
Tiny
CANNON1349
  • MECHANIC
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Hello, sorry for the delay, I had to wait for a valve to be delivered. With the new valve, I haven't seen it short cycle yet. When the fan turns on the compressor does shut off strongly, but it doesn't short cycle. Rpms still drop a good bit when the fan turns on. Also notice the same drop when the blower motor is turned too high. But, nonetheless it is doing better than before as it seems to handle the rpm change better.
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Wednesday, June 7th, 2023 AT 10:53 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

When you had the IAC removed, did you make sure everything was clean inside where it is mounted?

Let us know. Also, let me know how far the RPMs are presently dropping.

Take care,

Joe
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Wednesday, June 7th, 2023 AT 7:01 PM
Tiny
CANNON1349
  • MECHANIC
  • 670 POSTS
There was no blockage, but it's an old car so I could probably spend all day cleaning black colored stuff off the walls of the intake. The RPMs will drop to 650 or so when the fan kicks on, it seems like the new valve is helping the engine moderate that load.
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Wednesday, June 7th, 2023 AT 7:17 PM
Tiny
JACOBANDNICKOLAS
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Okay. If you feel it is working properly, that is good. If you still feel something is not right or creating an issue, please let me know.

Feel free to come back anytime in the future. You are always welcome here.

Take care,

Joe
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Thursday, June 8th, 2023 AT 7:37 PM
Tiny
CANNON1349
  • MECHANIC
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I am curious if there is an electrical test I can do for the fan, if there is a specific amount of resistance or if I can see if it is pulling too much voltage, however this car uses a 40A fuse for the fans so I would find it hard to blow.
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Thursday, June 8th, 2023 AT 7:59 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

On most digital multimeters (DMM), there is an amperage setting. In this case, you would disconnect the power wire to the fan motor (gray wire with a red tracer) and use the multimeter as a bridge between the power supply and the fan motor. In other words, power would run from the wire into the + terminal of the DMM and then out the - terminal of the DMM to the blower motor. When the motor is commanded on, the meter will provide the amperage draw by the motor.

I drew a sad excuse for a pic below showing how the DMM is tied between the power supply and fan motor. No making fun. I tried. LOL

Let me know if this helps or even makes sense.

Joe

See pic below.
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Thursday, June 8th, 2023 AT 8:53 PM
Tiny
CANNON1349
  • MECHANIC
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Is it possible to do this with the DMM plugged into the fuse location? I don't have a key to push wire terminals out of the connectors.
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Wednesday, June 14th, 2023 AT 7:47 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

You can do it anywhere that is part of the power supply circuit. As far as pushing pins from the connectors, that isn't needed. Just use the DMM as a bridge.

Let me know.

Take care,

Joe
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Wednesday, June 14th, 2023 AT 10:07 PM
Tiny
CANNON1349
  • MECHANIC
  • 670 POSTS
Hello, if we look at my first message in this thread, I mentioned the compressor cutting off 3 or 4 times until 30 minutes passed, then it doesn't do it. After replacing the IAC valve, the compressor cuts off only once, not short cycling. But again after 30 minutes all of this behavior stops.
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Friday, June 16th, 2023 AT 10:05 AM

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