A/C Only Works at Highway Speeds

Tiny
UPMM019
  • MEMBER
  • 2001 CHEVROLET SUBURBAN
  • V8
  • 4WD
  • AUTOMATIC
  • 212,000 MILES
So I have owned this 2001 Suburban since last October.

To my knowledge the A/C worked fine and had been working fine. However, the drain is clogged and I could never find where to blow it out.

Since the A/C is not working but when I am at highway speeds and have it on after about 10 Minutes the dash makes the suction sound and then the A/C work and she blows cold.

However, once out of highway speeds and in city drive it stops working.

I thought I'd try charging the system but when I hooked up the R-134a setup I have the meter read in the RED which means alert. It did not read low or normal.

Looking to see if anyone has suggestions to the problem.

I did confirm that at idle if you push the A/C on and off the clutch does not engage. However, like I said at highway speeds it works just fine.
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Saturday, June 21st, 2014 AT 11:26 AM

25 Replies

Tiny
UPMM019
  • MEMBER
After letting the vehicle cool down for most of the day I wanted to check it again.

This time when I started the suburban and turned on the A/C it worked and I could hear the clutch engaged but when it did it made a NOT normal noise. Almost a quick squeal of some sort but very very short. It did that a couple of times.

I hooked up the R134a charger again and this time in read in the RED but not as high as before.

I drove it for less than 10 minutes in town and it stopped working again.
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Saturday, June 21st, 2014 AT 4:03 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Are you sure that you checked on the low side of the AC system?
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Saturday, June 21st, 2014 AT 8:09 PM
Tiny
UPMM019
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Where is the low side located?
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Saturday, June 21st, 2014 AT 8:25 PM
Tiny
UPMM019
  • MEMBER
If this is the port then, yes, this is the port I hooked my R134a charger too.
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Saturday, June 21st, 2014 AT 8:26 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
That's correct. If the pressure is too high on the low side, either you have a clog in the system or the compressor itself is bad.
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Saturday, June 21st, 2014 AT 8:36 PM
Tiny
UPMM019
  • MEMBER
Can you explain why it works intermittently?
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Saturday, June 21st, 2014 AT 8:37 PM
Tiny
UPMM019
  • MEMBER
Would a plugged front A/C drain have anything to do with this?
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Saturday, June 21st, 2014 AT 8:38 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
The compressor COULD be going bad an causing the pressure on the low side to be too high. Also, the receiver dryer could be bad. Either of these issues could allow the unit to work sometimes and not others. Tell me this. Have you checked static pressure on both the low and high side? That is when the engine is off. Both sides should be nearly equal. When you start the engine, the low side should be around 30 to 35 psi and the high side 210 psi. Are you able to get me a reading with the gauges you have?
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Saturday, June 21st, 2014 AT 8:49 PM
Tiny
UPMM019
  • MEMBER
I could only do the low.

I don't have a manifold set, just the cheapo recharger for the low side.
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Saturday, June 21st, 2014 AT 8:50 PM
Tiny
UPMM019
  • MEMBER
Using the recharger low side, with engine off, it reads around 80psi.
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Saturday, June 21st, 2014 AT 8:55 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
That is still high. Knowing that leads me to believe the compressor is good and you may have a plugged (or partially plugged) receiver dryer.
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Sunday, June 22nd, 2014 AT 8:34 PM
Tiny
UPMM019
  • MEMBER
What would cause it to plug?

This morning the temps were much lower here and I did another reading and this time it showed low so I could add the R134a.

Worked good for two hours straight but then later today it stopped working again.

No strange noises this time.
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Sunday, June 22nd, 2014 AT 8:42 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Internal contaminates cause issues. As far as it working today, did the compressor stop engaging when it stopped?
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Sunday, June 22nd, 2014 AT 9:03 PM
Tiny
UPMM019
  • MEMBER
So the issue continued this past week. Took it to a local shop and today they said it needs a new fan clutch.

Please explain what that has to do with the A/C. I'm confused.
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Tuesday, July 1st, 2014 AT 7:42 AM
Tiny
UPMM019
  • MEMBER
So $175.00 later the shop says it was the fan clutch.

Feel like I was robbed to some degree.

$99 for a fan clutch

$36 to use the A/C gauges

$38 for labor

plus tax and some other $3 B.S.
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Tuesday, July 1st, 2014 AT 12:23 PM
Tiny
JACOBANDNICKOLAS
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Did that fix it?
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Tuesday, July 1st, 2014 AT 6:07 PM
Tiny
UPMM019
  • MEMBER
Well no, in fact it did not.

Same issues as before and I am $175 in the hole from a fan clutch that probably didn't even need to be changed out.

Calling the shop today to complain and hopefully get another appt to have them fix it. Though I don't have high hopes.
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Monday, July 7th, 2014 AT 5:08 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
I really didn't think that would do anything. I still feel it is in the receiver dryer. Let me know what you find.
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Monday, July 7th, 2014 AT 7:56 PM
Tiny
UPMM019
  • MEMBER
Yeah, I think he just quickly changed the fan clutch and didnt check squat after that.

Sorta of BS in my opinion.
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Monday, July 7th, 2014 AT 9:06 PM
Tiny
UPMM019
  • MEMBER
Why do you think it is the receiver dryer?
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Tuesday, July 8th, 2014 AT 5:52 AM

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