Help please with A/C troubleshoot

[Panoscopic]

Last summer, I did a R134 swap. Had a tech do it - full evac, new oil, etc. It seemed to run fine, but not as cool as I would have liked it. One thing that bothered me was that it seemed to cycle more than it should have - just as the air would get up to a good chill, it would cut off.

Well, this spring when I turned it on for the first time, the compressor did not engage. So, I did a little troubleshooting myself and found that if I bypassed the low pressure switch (I think that is what it is, the switch just by the view glass on the right fender). When I bypass the switch, the compressor engages.

Not really wanting to mess the A/C, I took it to a local shop that is supposed to be very reputable and recommended by a friend. He did an inspection and later told me that the there was a leak in the evaporator. When I asked him why the compressor did not engage, he said that it was because of the low pressure of the system.

This is does not make any sense to me based on my past experiences. I thought that no matter what, even if there is little no refrigerent in the system, that it will run anyway. My intuition is that the problem is the low pressure switch and that the rest of the system is fine.

He quoted me a price of $900 with labor to fix it, and I about choked. I'm afraid to go to another shop if this guy is really trying to frisk me.

Any ideas or recommendations???

[Santa Claus]

The purpose of the low pressure switch is to keep the compressor from engaging if you are in fact low on refrigerant. This keeps the compressor from burning up. If he wants that kind of money for a new evaporator and service I think I will go back into the wrenching business. I would definitiely get another estimate.

[Stolen76]

I'll second that ! Your evaporator shouldn't run more then $150, and that's high !

[gwinn]

Okay! The low pressure switch is what controls the temp in your cab. When the refrigerant charge is correct, your compressor will cycle on this pressure switch. The pressure within your a/c system corresponds with the temperature of the refrigerant. As the circulating air cools down so does the refrigerant, and your low side pressure drops until the pressure switch opens and stops the compressor. When the air warms up it closes the switch. If your low on refrigerant, your pressure will also be low, which opens the pressure switch prematurely. I'm not an automobile refrigeration tech so I could be wrong. Question! Did the technician actually find the leak in your evaporator, or is he assuming it's there because he can't find it? $900 is very steep for this repair. I don't think the dealer is even that high! Get another opinion if you can!

[ June 21, 2002, 09:55 PM: Message edited by: gwinn ]

[TexasJ10]

The pressure switch's sole function is to keep the compressor clutch from engaging if insufficient refrigerant is in the system. On a 134a system the site glass is useless because slight bubbles are present even with the correct charge. $900 is way too high for a repair. I would definitely seek a second opinion and find an honest shop to do the repair. Alternatively, ask a shop to remove the remianing 134 on a Saturday morning, replace the evaporator yourself in about 2 hours, then take it back to them to be evacuated and recharged. If you open the system you should also replace the drier but make sure they give you one for 134a refrigerant.

If it is a slow leak you could also buy a stop leak product and, with a simple kit you can get at Walmart or kmart, you could add a can or two of 134a yourself and see how long it cools before it leaks out. 134a is readily available for $6 a can and the kit is usually only $20. This would be the cheapest way to go.

[Stolen76]

If he can't point to the leak and show you a wet spot, go get someone to dye-test the system. Most places can do that for about $35, well worth it as it will find a leak as small as 1/4 ounce per year. I was thinking condensor in my first response. The last post was right, a lot of guys will point to the evap when they can't find a leak because it's enclosed in a box and when they stick their halogen leak detector in there it goes nuts. It could also be an expansion valve or fitting leaking, which he would also be relacing while he was in there and you'd never know which part was actually leaking. From his standpoint it's a very safe diagnosis !

[Panoscopic]

He claims to have found the leak with a "sniffer" and did not actually get into the evaporator.

You guys gave me lots of good advice. I think I'll assume there is a leak and either try another shop or try to find the leak myself.

[Ernzo]

Texasj10 is right, circumventing the low presure switch is a simple way to isolate either a bad switch, or low presure. If your system is dry you can easily replace various O rings. Just simply tighten the fittings as well.

I would get some R13, fill it up (remember to follow the instructions) and see if it blows cold. If it does, use it until it stops cycling, this may be all summer long!!

Do not know if there is R13 stop leak, but my experience was nill, nogo, waste of $. Maybe others have had luck.

[gwinn]

It looks like I might learn something from this thread too! How is the temperature controlled in the cab? Is there a T-stat in series with the LPS? Is the t-stat also a thermal pressure switch? Where is it located?

[TexasJ10]

There is a tempature control switch that has a probe that is inserted in the evaporator fins. This switch will also cycle the compressor clutch.

[Stolen76]

Like I was saying, if he used a sniffer you could just have an o-ring leak. Get it dye tested and be done with it !

[Panoscopic]

I think I want to open up the evaporator housing and make a visual inspection. It looks like it is fairly easy to access. Anybody have any experience opening it up?

In the absence of a dye test, if I inspect the evaporator visually, would I be able to see any evidence of a leak, like compressor oil?

[TexasJ10]

It's a little more difficult than it looks to open it up. The hoses will not stretch very far. The connections to the hoses are one of the most likley leak points and I think you can see them behind the evaporator box next to the fire wall. It sound like your leak is not very big since your system still has 134a in it. The refrigerant gas can pass through areas that the oil will not. The dye test is very inexpensive and is a much better way to go. I still also believe that you may be fine by simplying adding a can of 134a with the dye. If you can't find the leak, it may only occur when the outside temperature is cold. The additional can of 134a may easily last you all season.

[Stolen76]

You can dye test yourself too. The cans with the tracer dye in them are only a couple of bucks more and in place of the fancy light you can use a Streamlight Stylus in ice blue. They run $20, but you could charge that to someone else to do theirs! They work well and even better with what they call UV enhancing glasses, they look like target shooters yellow glasses. Anyway, the light and a can of freon with the dye in it should only run about $30 total.

http://www.streamlight.com/2001/stylus_specifications.htm

[Panoscopic]

An update here.....

I got the leak detector in. Turns out it was kind of unnessasry as it started just gushing out of the low pressure side after the evaporator, just before the compressor inlet. I looked at the hose - there is a huge gash on the bottom side of the hose. I'm wondering how it got that way - there does not seem to be anything that could have rubbed it that bad. The outside black covering is cracked off, and the meshed fiber inside is ruptured.

Its there a way a low pressure hose could rupture like this? Isnt the low pressure side only something like 20 pounds pressure? I can't help but think there might be some hanky panky with the shop that inspected it. What is funny is that he told me that there was a leak in the evaporator, and he never mentioned anything about the retun hose. It does not look quite like a cut, but if go back to complain, I better pretty sure if I am making acusations.....what do you guys think?

Anyway, regardless, I will need a new low pressure hose. I was wondering, what is my best option? A wrecking yard or try to buy replacement? Would a replacement be expensive or hard to find?

[2j20's]

I just had one made myself from a a/c shop 27.00 bucks tax and all.

[oldyellowwagoneer]

An a/c low pressure hose is only at 20 psi(more likely 30-35) when the compressor is running, otherwise the entire system will even out which will put alot more pressure in it. Being as the hose is as old as it is, it is very possible that it ruptured as described. If you dont feel comforatble with that shop go somewhere else to replace it. Also, if you did the conversion without replacing the reciever/dryer with an r134 compatible replacement that could be causing the not as cool feeling. Replace the hose and receiver/dryer, then evacuate for at least 40 minutes before re-charging. Start the re-charge with about 80% of the r-12 capacity first. If its not cold enough for you then add 5-10% more.Don't fill to the original capacity.If you over fill with r134 it will not cool as much. DENNIS

[Stolen76]

If there is a goodyear rubber store or parker hose dealer near you, check them out. The hoses are less then 1/3 of what you will pay for an actual replacement item. You can go to http://www.parkerhose.com to find a dealer

[steven79]

One note here try to find freeze 12 or some other freon for it. The york compressors will not hold up to 134 for long they are not built for the pressure it runs plus the hoses will not last long. i got r12 in mine and you can hang meat in my wag, could not cool it with 134, just did a friends cad with freeze 12 and it works great.
freeze 12 (http://www.freeze12.com/)
i did this with no differant tools the r12 side can tap fits these cans.