Intermittent A/C

[lsupcar]

My a/c will sometimes work normally, but othertimes will experience a one to fifteen minutes delay, in which time, while on auto, no a/c'ed air will be blown, and then, when it starts working and blowing cold air, it might cut out for another minute or two before coming on again like normal.
I have searched and found others complaining of these symptoms, but no one has posted a cause that led to a resolution.
I've recently had a new compressor and drier installed and will likely take it back to the shop to be seen to again, as this was a problem that has been occuring for a year or so and the repair was only about two weeks ago, but I don't have time right now to bring it back in.
If someone has a solution to this problem I would appreciate the help.
Thanks.
Bill Z

[Manarius]

Sounds to me like a refrigerant charge issue. Either the refrigerant is undercharged (the most common case) or it is overcharged.

In the case of undercharging, the compressor will not turn unless the system senses enough refrigerant in the system. Perhaps your system is just on that edge and that's why it's going off.

Overcharging, well, it's going off because it's over-pressurized. A set of a/c gauges could probably help you figure this one out quick.

[92snowmachine]

is your ac r12 or r134a. if it's the new stuff you can buy a recharge hose kit that screws on top of the can and hook it to the low side to see what your pressure is from this reading you can figure what the high side is as well. they sell around here for about 10 bucks.

[alia176]

I'm bringing this to the top as my symptoms seem to match the original poster's. However, in my case, the HVAC diagnostic revealed code 14 & 15.

Code 14: evaporator sensor open
Code 15: Refrigerant temp sensor open

I'll check the two connectors on the evap box to make both are connected.

I converted the system to R134a and replaced every single component. The evaporator is about three years old along with a new expansion valve. The compressor is one year old and it's brand new. I did all the work and made sure all sensors are in their respective locations inside the evaporator housing.

Last year, I had an a/c shop recharge the system with R134a and she ran very nicely. This year, I'm having the symptoms described on post #1.

Anyway, I'll report back with my findings. Refrigerant charge is good, maybe a tad too high. I did manage to put in a can of R134a and maybe I shouldn't have. The low side pressure was a tad low for the ambient temp so I sucked in a can. In retrospect, I should've resolved the diagnostic codes before introducing this variable.

Thanks for any inputs.

[92snowmachine]

what pressure where you at and what was the ambient temp?

[SpecialFX]

I have the same issues. It works 90% of the time, but sometimes does the same as the OP. My car is a big question mark though as I've had it less than a month. I'm interested in seeing if anyone figures this out!

[alia176]

Originally Posted by 92snowmachine

what pressure where you at and what was the ambient temp?

Good question and this is where it gets dicey.

When the system refused to turn on last month, the low and high pressures were about 120 psi with ambient temp around 75°. The comp wouldn't run on this particular day.

Two days ago, the same thing happened and I watched the comp while the gauge was hooked up to the low press side. I used the cheapo gauge that comes with the can. This is more portable and easy to use when I want to do a quick check, while I'm running around doing errands, to see what's going on. The low pressure was 130, ambient at 80°. The comp would cycle on for about ten seconds and the pressure would drop to approx 40, and then shut off and pressure return to 130.

Yesterday, ambient temp was around 82°, the a/c system ran perfectly all the way home. No issues what so ever Vent temp was at 60°.

According to this linkie, high pressure at the low side could be one of three things:

- Expansion valve opened too wide (mine is less than five years old)
-Heat sensitizing tube faulty contact (this could happen, I suppose)
-Too much refrigerant ( I did add a can of r134a last month)

Attached is a pic of my evaporator before re-installation.

I'll take my manifold gauge to work today and hook it up at lunch to see what's going on and report back with more concrete numbers.

Thanks

[92snowmachine]

it does seem like the system is overcharged if the pressure was that much higher than the ambient temperature, however this can happen for other reasons so it would be important to get the high side reading from the gauge set as well. the capillary tube tends to not be a likely culprit and the expansion valve itself rarely fails. your compressor may be short cycling because when it kicks on and sucks down the low side the high side pressure are extreme. this can cause it to turn off and set codes in the system as well. not sure what the exact cut off is on the svx but many systems will turn off the compressor if the high side pressure exceeds 300-350psi. then the system won't run because of the stored codes but eventually runs again after it sees enough drive cycles without another issue.

[lsupcar]

As a follow up to my original post, I had my system rechecked by the shop and all parameters checked out ok, and they said the next step was tearing into the dash as they were getting a code for the light sensor. I did not think that was a likely cause so did not pursue it further as the system worked ok for the most part.
I did receive a PM from a member with a similar problem, who said his problem was fixed with a new a/c control unit in the dash. I will try that if the situation worsens over the summer.
Bill

[Green1995SVX]

The car will always throw a code for the light sensor unless the car is in direct sunlight when the codes are pulled. This is normal.

[alia176]

I did some more followup yesterday. The ambient temps were cool so the high and low pressure readings were not stellar. Still, maybe you guys can get some ideas from the #s.

Ambient: 72
Low: 5
High: 65

The compressor ran for a little bit and then stopped.

I went home and played with the diagnostics of the climate control. Code 14 & 15 kept returning so I'll follow the troubleshooting steps outlined in the FSM this weekend. The glove box needs to come out so I hope to tackle it today or tomorrow.

[alia176]

The temp at the house reached 75 degrees so I took the opportunity to compare the SVX low press reading with another vehicle, '97 landcruiser.

SVX:

low press: 90 psi
engine running
a/c fan on HI, windows open
clutch: did not come one

Landcruiser
low press: 30
engine running
a/c fan on HI, windows open
vent temp: around 60°. Probably a tad low on R134a

I'm experiencing code 14, 15 so I'll need to find the time to remove the glove box and do some troubleshooting using the FSM steps.

[alia176]

Ambient temp was 87º yesterday and the low press reading was at 30 psi (should be 45-55 psi based on 85º ambient). The low pressure came up to almost 40 psi at 1500 rpm after I added one full can to the system and the vent temp was 60º. This is not close to being great but acceptable while driving around.

Haven't found the time to tear into the dash yet unfortunately and won't have time until two weeks from now. I'm getting ready to go camping/wheeling for a week in SE Utah so that's been monopolizing my time.

[Tapani]

With the variable discharge compressor the pressures will not read the same as in "ordinary" cars. The compressor will do only the work required (requested by the AC controller) to reach the set interior target.

BTW What is the OEM part number for a brand new compressor? Is there only one (R134a) available for all year models? Where did you get yours from?

Tapani

PS Have you taken apart the old compressor?

[alia176]

I have yet to take mine apart Been busy getting ready for a week long camping trip in the remote part of Utah.

When I ordered my unit, I got one for a '96 SVX and the cost was much less than one for a '92 SVX.

http://www.dealerdirectparts.com/Sea...fineBy_92=8900