R4 compressor NEVER cycles

Friendly format provided to inquire about automotive a/c systems.
Archived Forum

Moderators: bohica2xo, Tim, JohnHere

eb4tx
Posts: 7
Read the full article
Joined: Thu Oct 05, 2017 9:18 am

R4 compressor NEVER cycles

Post by eb4tx »

I have a 1995 Suburban in excellent condition. A/c system cools well BUT, the compressor clutch never cycles. I mean NEVER. Driving around under 30 minutes I can see 40 degrees out of dash vents on a 90 degree day. But, on a longer drive I believe the front evaporator starts to ice up. I will start to have condensation on the inside case. I have changed the pressure switch on the accumulator and the pressure switch on the condenser. Both ACDelco OEM switches. I have had the system evacuated twice in the last year just to make sure the amount of R134a was correct. Both times system levels were spot on correct. My situation is I live an hour drive from any nearby town. I have been to several a/c shops and with no solutions. I'm a pretty handy mechanically, just don't have any a/c gauges or tools. I guess I shouldn't complain as system does cool well, but knowing the clutch should cycle and it doesn't has me very concerned. Any thoughts on why the clutch NEVER cycles?
Dougflas
Posts: 379
Joined: Mon Apr 18, 2016 6:10 pm

Re: R4 compressor NEVER cycles

Post by Dougflas »

need to know ambient temp. if it is hot enough, the compressor will not cycle due to heat load. low airflow may cause evap to freeze. tape manifold to windshield and indicate pressures. without checking system, you may have a defective cap tube switch in the evap or it may not be in proper location.
User avatar
Cusser
Preferred Member
Posts: 846
Joined: Sun Apr 24, 2016 6:29 am

Re: R4 compressor NEVER cycles

Post by Cusser »

I don't have my 1988 or 1994 Suburbans any longer that had R4 compressors, but I'm not positive that these systems were made to cycle; like maybe running full time and one would just blend in some heat if the vent temperatures were too cold.

If you're in a humid-enough climate, wouldn't you notice evaporator freeze up by decreased VOLUME of air coming out the vents?

And couldn't you switch the compressor OFF manually with a dash switch like for a minute every 10 minutes to allow any ice to melt and drain out the condensate tube? Let's assume that the condensate drain is not clogged.
User avatar
JohnHere
Preferred Member
Posts: 1196
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: R4 compressor NEVER cycles

Post by JohnHere »

I'm wondering, though, whether the evaporator is actually freezing up. When you think it is, do you also notice a marked reduction in airflow from the vents along with a change in sound from the blower?
Member – MACS (Mobile Air Climate Systems Association)

Thankful for the responses you have received? Please consider making a monetary donation to this Forum.
eb4tx
Posts: 7
Joined: Thu Oct 05, 2017 9:18 am

Re: R4 compressor NEVER cycles

Post by eb4tx »

First off, I live in Central Texas, it's end of May and it's 90 degrees by 11am. This is the description that GM states for a 1995 Suburban: "The A/C system is a Cycling Clutch Orifice Tube (CCOT) type with a fixed displacement compressor and pressure cycling switch to control evaporator temperature". So yeah, its suppose to cycle. As for as the evap freezing up, just a guess as interior a/c case starts to sweat and drip. Also the drain tube flows like a river outside via the drain tube. Drain tube is NOT clogged.
eb4tx
Posts: 7
Joined: Thu Oct 05, 2017 9:18 am

Re: R4 compressor NEVER cycles

Post by eb4tx »

Photo of 1995 Suburban. 145k miles. I'm the second owner.
IMG_0694.jpeg
IMG_0694.jpeg (137.37 KiB) Viewed 7450 times
Attachments
IMG_1345.jpeg
IMG_1345.jpeg (85.25 KiB) Viewed 7450 times
User avatar
bohica2xo
Preferred Member
Posts: 1170
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: R4 compressor NEVER cycles

Post by bohica2xo »

If you pull the connector off of the cycling switch, does the compressor stop?
eb4tx
Posts: 7
Joined: Thu Oct 05, 2017 9:18 am

Re: R4 compressor NEVER cycles

Post by eb4tx »

@bohica2xo. " If you pull the connector off of the cycling switch, does the compressor stop?" Yes it does. Plug connector back in, clutch engages compressor.
User avatar
bohica2xo
Preferred Member
Posts: 1170
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: R4 compressor NEVER cycles

Post by bohica2xo »

So it can cycle, you just never get enough liquid built up in the accumulator to drop the pressure.

GM used an insulator for the accumulator on some models. Part number 15-10614

Might give that a try.
eb4tx
Posts: 7
Joined: Thu Oct 05, 2017 9:18 am

Re: R4 compressor NEVER cycles

Post by eb4tx »

When I acquired this vehicle 4 years ago, it had the original foam fitted cover on the accumulator. The a/c worked fine when I got it, except I noticed the clutch never cycled then as well. That original R4 eventually developed a leak 2 yrs later and had to be replaced. Replaced compressor, and accumulator together at the same time. That original cover had deteriorated and was not in great shape so it was not put back on. So the issue of no cycling was present for 2 yrs with accumulator cover and now without the cover. I appreciate your suggestions hopefully we can sort this issue that has dogged me for 4yrs.
Post Reply