A/C compressor cuts out and on at high speed

Tiny
MACHINIST?
  • MEMBER
  • 2006 KIA SEDONA
  • 2.5L
  • V6
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
Some say that is normal but I don't like it. The expansion valves seem to do a good job which leaves the discharge pressure as indicator of correct charge. It goes up or down by 50lb at idle or 2,500 rpm's. If I have it over charged the pressure switch can cause the cycling. What should the discharge pressure be at what rpm and ambient temperature?
Friday, February 28th, 2020 AT 9:39 AM

5 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
Compressor cycling is normal. What are the intervals for it cycling on and off? 50 psi cycling drop is high. At 80 F you would expect the low side to be at 40-50 psi with the high side running 175-210 psi. If you are seeing a 50 psi drop I would suspect a low charge more than high, or a blockage in the system that is slowing the return of refrigerant to the compressor. My first step would probably be to check the pressures, then pull the charge out, vacuum the system, then recharge with the OEM charge of 32 oz. Of R134a and check the pressures again.
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Friday, February 28th, 2020 AT 11:34 AM
Tiny
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I agree 32 oz. Of R134a and dun unless there is a blockage. With my shade tree tooling 32 oz is not going to be easy. I did bolt an old compressor to a board and belt drive with a washing machine motor through a reduction pulley. Worked good til I had too many hoses go bad. It may be a couple weeks til I see 80 F. My chart shows pressures at 70 F, but does not, like you, mention rpm. My discharge pressure goes up by 50 lb from idle to 2500 rpm. It's okay. I can get it right by trial and error. I was just short of time the other day. Thanks anyway.
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Monday, March 2nd, 2020 AT 7:43 PM
Tiny
STEVE W.
  • MECHANIC
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There won't be any RPM listed for a vehicle because of the differences in compressor designs and applications. For a 70 degree day you should look for a low side of 35-40 and high side of 145-160. Compressor speed isn't listed simply because it isn't a constant. Is this compressor on a car or are you trying to put together something like an air compressor using the components?
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Tuesday, March 3rd, 2020 AT 7:29 AM
Tiny
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I did bolt an old compressor to a board and belt drive with a washing machine motor through a reduction pulley. I used it to pump 134a to a old propane bottle in a bucket of salted ice. I had pre-vacuumed the bottle three times. When I was dun changing a compressor I vacuumed the system and put the old 134a back in with the compressor on a board. It worked great. My problem with this Sedona is at freeway speed. I am wondering if I have a bad pressure switch? Some pressure switches have a Schrader valve under them. Can you tell me if this one does or not?
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Thursday, March 5th, 2020 AT 4:07 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
It does not have a schrader valve.
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Thursday, March 5th, 2020 AT 8:23 PM

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