AC short cycling. Anyone replaced the evap expansion valve?

[kkrover]

AC has not been working well. It is especially bad on the highway. It will blow cold, then cool. My mechanic checked the system and said refrigerant is fine, but it does short cycle, especially at higher speeds. They said it is the expansion valve in the evaporator getting clogged.

Anyone delt with this, or better yet, anyone done the repair? They said could be upwards of $700 to fix. For that I'll put the windows down...too bad it hotter than hell here.

[carlosz]

I converted my 92 to R134 alittle over a year ago, all I did was the retrofit kit from atlantic british, it included the R134 heads, seals and accumulator for about 150.00 I think the pressure valves gor for under 100.00 bucks each.
$700.00 bucks? someone in that shop wants a little extra for their vacation this summer.

[sven]

The 95 RRC is already R134.

[carlosz]

I know that, I was simply giving an example of parts cost.
certain 93's and 94's in "the great state of cawlifonia" (arnold's words)
did begin to comlpy with the R12 ban quite early, the new buyer was being given the option of a/c gas type in order to get people used to the "new" a/c
Carlos........

[kkrover]

their reasoning for such a high cost was the time and labor to access the evaporator to switch it out. They say it is much like going for the heater core, in that you have to remove much of the dash to get to it.

Anyone know of any shortcuts to access the evaporator or have dealt with this before?

Also if the low side is low and short cycling, can it damage the compressor? I can prob. live with it the way it is, but don't want to have to replace the expansion valve and the compressor

[carlosz]

for a somewhat quick fix, try putting a vaccum onthe system, about 20 t0 25
inches for about 30 minutes minimun should give you decent results.
if the problem persists then you may have to fork it over.

[roverandom]

Sorry, no such thing as a quick AC fix. If there is, it will not stay fixed for long. Remember the shop is not just charging you parts (plus mark up) and labour. They are also charging you for use of the equipment etc. etc. It is how they pay their bills. The equipment needed to work on AC systems costs a lot of $$$. So as above, you may just have to pay up as most likely all the shops in your area will charge the same (or close). But for a low buck solution you can go with the old 4/60 AC!

[Sign Guy]

British Limited has the expanson valve for about $75 (iirmc). I've got the same issue and will be persuing it soon. I am planning on pulling the dash apart and just leaving the tech stuff for my shop.

[lrsafari]

It was a few years ago, but it is buried about the evaporator.

I went into a generic auto ac parts warehouse and they matched it to a generic part. I seem to recall it cost me $27. I MAY be tearing into the dash this weekend, and if I do I will see if I can get a part #/manufacturer of of it.

Scott

[kkrover]

a random thought leads to a randowm question: Why would it cycle out much more quickly on the highway vs. around town? Seems to work ok around town, but can't keep up on the highway.

[roverandom]

The system is short cycling more on the hwy than in town because of the thermostatic switch. The switch acts as a de-icing control by disengaging the compressor if the evap pressure goes too low and ice begins to form on the evap fins. As the evaporator air temp approches freezing, the switch opens the compressor clutch circuit and dissengages the clutch. As the temp begins rising to a pre-set value the electrical switch closes and the compressor operation resumes. So, driving at speed on the hwy the evap is cooler and it short cycles more often due to the pressure/temperature difference ( because of the clogged valve) and thus, icing occuring. In town, you will have less airflow and a much warmer evaporator, so no icing occurs (even with the clogged valve) and the compressor works as normal. A long answer to a short question. Hope this makes some sense to you.

[roverandom]

Originally Posted by kkrover

a random thought leads to a randowm question.

and the reply is by roverandom! How apt.

[stevo-II]

hmmm....that would suggest that the system is cooling well enough to form ice on the evaporator, which it sounds like its not according to his first post, but roverrandom could still be correct if the thermostat has gone bad and is causing it to short cycle long before it reaches freezing temps (although he did say it cooled fine around town).

My guess is that you do have a clog in the line or in the expansion valve - the worse news is "where did the stuff that is clogging it come from?" Not sure if your truck has it or not, but a lot of vehicles have a switch on the low pressure side of the system, if the pressure drops too low, then the switch opens and cuts off the compressor to protect it - i.e. assuming you had a leak or something. Now if you have a clog at the expansion valve (it could just be moisture in the system forming ice inside the valve) - or just a bad expansion valve, the compressor will run and the high side pressure will continue to climb and load up with condensed liquid until the low side pressure drops to the point that the low pressure switch kicks the system off. Then it will equalize, the switch will close and the cycle starts over again. It happens more at highway speed because your now spinning the compressor at a higher steady RPM, the pressure differential builds up and bingo, the system kicks out. That would also explain the poor performance of the system - not enough refrigerant is passing through the system.


Have somebody put some guages on it - if the high side is too high and the low side drops to nothing, then you've got some kind of restriction. If thats not the case, then suspect the thermostat in the evaporator...

The more I think about it, your symptoms sound suspicious of moisture in the system.....that moisture will eventually form ice inside the system - usually at the expansion valve and cause a clog - perhaps have somebody drain the system, put in a new dryer, pull vacuum and recharge?

I hate A/C problems, sometimes they are so hard to diagnose...


Steve