1995 Honda Civic DX - Air Conditioning was cycling on-off about every 30 seconds. Gauges indicated low side was about 40 and high side was about 350. It was about 90 degrees outside. Thinking blockage we changed the expansion valve and filter/dryer, vacuumed the systems, and installed 16oz (about 1 ¼ cans) of 134. At idle the low side was 35 and the high side was 200. With increased RPM (2500) the low side drops to about 25 and the high side jumps to 350, the vent temp was about 60. The AC then started to cycle on-off after running for awhile. We then evacuated some of the 134, the AC stayed on (stopped cycling). The low side was about 20 and the high side decreased to about 325. The vent temperature also increased to 70. Through all of this the condenser fan cycles on-off on sporadic intervals.

Any thoughts on the cause of this excessive high side pressure?

Thanks,

 

sometimes the heat outside alone can cause the highside pressure to increase but it shouldnt increse such a signifigant amount and it also makes sense it increases under increased throttle thats normal as well and it is also very normal to only expect to see your ac temp coming out of the vents at a 30 degree difference from the outside air for example:90 outside you should see 60 and below come out of the vents....also check your compressor switch relay that might be whats wrong.

 

Let me give you a few of my thoughts...

I live in Arizona - it's 106 degrees outside as I type, heading for 112 - just another day in paradise.

I've worked on a LOT of A/C units, residential and automotive - it's just part of life around here - either that or let the HVAC guys bend you over the fence...

Automotive A/C compressors are supposed to cycle on and off - that's what they do.

IMHO, 350 on the high-side is perfectly normal. I don't start worrying until it gets 425-450ish. When it gets too high, your compressor will tend to stick at stoplights and so forth, so you're better off, in this heat, running it a little low.

If anything, going by your figures, your A/C is probably cycling on n' off because you don't have enough pressure on the low-side. I *think* the pressure switch on a Honda will cut-out @ 30 PSI low - 450 PSI high, so...

The only other thing I can think of is - your evap might be clogged up with leaves and freezing up from poor air circulation and/or the capillary temp sensor is touching the evap itself and *thinking* its frozen up.

Anyway, happy hunting!

 

Looking at other similar postings and via a mechanic friend of mine I was under the impression that the high side pressure should be no more than 200psi. My mechanic friend thinks there is blockage somewhere hence the reason for replacing the filter/dryer and expansion valve. When the AC cycles on-off it does it about every 30 secs. The AC puts such a load on the engine that when it cycles as you drive you can really tell that its happening.

It appears there is only a pressure switch on the high side which I'm told is for turning the condensor fan on-off, is this correct?

There was alot of leaves and such in the evaporator area, but they were cleaned out when the expansion valve was replaced.

Thanks,

Joe

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jnelson31 &raquo;</TD></TR><TR><TD CLASS="quote">Looking at other similar postings and via a mechanic friend of mine I was under the impression that the high side pressure should be no more than 200psi. My mechanic friend thinks there is blockage somewhere hence the reason for replacing the filter/dryer and expansion valve. When the AC cycles on-off it does it about every 30 secs. The AC puts such a load on the engine that when it cycles as you drive you can really tell that its happening.

It appears there is only a pressure switch on the high side which I'm told is for turning the condenser fan on-off, is this correct?

There was a lot of leaves and such in the evaporator area, but they were cleaned out when the expansion valve was replaced.

Thanks,

Joe</TD></TR></TABLE>

Hrm...

Well, here's some more thoughts...

Your high-side seems normal to me! Your low-side seems low - based on your numbers.

AFAIK, nobody uses a separate filter and dryer these days - its all in a single unit - called an accumulator.

The expansion valve, by definition, produces a blockage - that's normal - but you said you replaced that, so I can't image it being bad.

Once again, an automotive A/C compressor is supposed to cycle. Every 30 seconds or so sounds normal too, unless you live in a hell hole like me - then every minute or two is more normal.

Putting a load on the motor is normal also - especially on a Honda. If the head is locking up on you, and the drive belt is smoking on the clutch pulley - that's a totally different situation - a sure sign that you've overcharged the system - but you didn't mention that, sooo...

Don't know about a Honda pressure switch, but it probably cuts off at 450 on the high-side and 30 on the low-side to preserve the compressor in case of extreme over or under pressure. The only other cut off points are the evap capillary temp sensor and manual override on the cabin control panel.

I suppose its possible that you have some metal floating around in your system, if you've puked a compressor in the past - clogging up your expansion valve, but this is rather unlikely.

What I do, if I lose a compressor is - flush the system out with WD-40 - I flood it actually - then blow it out with compressed air, until the WD-40 comes out looking clear. Then I replace the accumulator, expansion valve and compressor - vacuum the system down for several hours (the longer the better) then charge the system. That way you KNOW you got all the metal out of the system.

Anyway, everything you described sounds normal to me, except I *think* you've slightly under-charged the system - but its hard to tell without actually being there - you know?

 

Check the condenser for damage. If it's getting insufficient airflow, your high side pressures increase. Ideal gas law and all that.

Spray it with a hose with the system running and watch the pressures / vent temps.

 

Oh come on, you might as well keep your "thoughts" to youself. 400psi is WAY too high and the compressor is NOT supposed to cycle every 30 seconds. Most older hondas (r12) have a high cutout switch set to about 390psi and low doesn't cut in till arround 10psi. There is also a thermometer/thermostat on the evap coil that will also cycle the compressor if the temp on the coil gets below 38f which it can if undercharged and there is too much flow over a small portion of the evap coil.
As for the wd40 flush, well, I'm just speechless. tell me you're not using a cammel and two bricks to evacuiate the system.



Then 200psi is only normal on a cooler day at idle too. AS he replaced the expansion valve and drier/accumulator then there still has to be some blockage in the system, . Might try cleaning the condenser as they tend to get dirty and will cause higher than normal head pressures. Sometimes too much aoil can cause high head pressures too, might evac it, flush it out well, and recharge in the normal way. add r134a with oil already in the same can, it will give you the correct amount.




Modified by itsmejto at 5:17 PM 6/17/2008

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by itsmejto &raquo;</TD></TR><TR><TD CLASS="quote">As for the wd40 flush, well, I'm just speechless...

Sometimes too much aoil can cause high head pressures too, might evac it, flush it out well...</TD></TR></TABLE>


Do tell?!?!?

What do you use to flush A/C systems?

 

WD40 will leave an oily residue, needs to be a compatible solvent that will remove that sticky black stuff from all internal parts. I disconnect everything and flush each part out individually, very important if your compressor vanes cracked up. Don't want any of those little chips getting back into the new compressor or expansion valve orifice etc.
Always Install a new drier/whatever one calls it nowadays, a $30 insurance.

 

My A/C runs great on the highway 45mph and greater. Around town it cycles a lot and sometimes stays off. Took it to the mechanic and we notices that the fan is not staying on thus the compressr is getting to hot and the pressure is getting to high.

On the highway I get enough air passing by the compressor to keep it cool enough.

Good luck

 

hond'as service manual say it should have 21-23 ounces, and if you went to 134 it should either be the same or 2-3 ounces less, but 16 is definatley undercharged.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fastrc2 &raquo;</TD></TR><TR><TD CLASS="quote">honda's service manual say it should have 21-23 ounces [of refrigerant], and if you went to 134 it should either be the same or 2-3 ounces less, but 16 [ounces of refrigerant] is definitely undercharged. </TD></TR></TABLE>


Exactly!

Thank you...

On top of that, they bled off some gas so they got less than 16 ounces!