Freshly repaired A/C system short cycling.

[gabton]

I recently proceeded to repair my AC system on my Honda Civic 2012. I replaced condenser, dryer, compressor and expansion valve. A/C has been working well except almost always short cycling (about 20 seconds on then 3 seconds off).

When it comes to filling this car with refrigerant, i've found conflicting information... I've seen charts saying 13.4Oz to others saying 15Oz I used one full 400g (14Oz) can at first. I had some loss in the hoses so I thought this would be fine. Since most of the post I've seen say short cycling is caused by low refrigerant, I added a little more. I still have the same issues and here are some of the reading I've got:


Test 1 - IDLE cold start
Ambient Temperature 80F humidity 80%
Low 30
High 160
NO SHORT CYCLING

Test 2 - Idle after 10 minutes (see https://youtu.be/TNBqRaZMNmo)
Ambient Temperature 80F humidity 80%
Low 28
High 170
SHORT CYCLING

Test 3 - 1500RPM (see https://youtu.be/_evn7X4JLuw)
Ambient Temperature 80F humidity 80%
Low around 15
High around 200
SHORT CYCLING

Other details
AC seems to cool fine with vent temps of around 40F degrees
Liquid line is higher than ambient temp
Suction line is sweating and cold
Fans are running
The compressor always seem to be short cycling when not in idle



Where should I go from here ? Does this look like an issue of charge or something else ?

Could the problem be with the expansion valve even though it's new ? Liquid line pressure seems a bit high and suction line seems a bit low. Also it seems like the recovery time when shutting off the engine is a bit slow (see https://youtu.be/oxg-_JM3ik0)

Could this also be normal? I just bough this car and I don’t know how it was behaving when the AC was working before.

[JohnHere]

Testing A/C performance at idle speed doesn't tell us much of anything because the compressor is doing virtually nothing. Better to test at an engine speed of ~1,800 RPM, set to Max A/C, blower on Medium or High, airflow set to Dash Vents, doors and windows open to maximize the heat load. Let the system run like that and stabilize for ~ 2 minutes, then check pressures and center vent temperatures while the compressor is engaged.

Even so, cycling the compressor as you describe would be considered normal on, say, a 90°F day. (I don't think you mentioned the ambient temperature.) With the compressor engaged at 1,500 RPM, it looks to me like the LS pressure is hovering around 30 PSI, also considered normal, as is the center vent temperature of ~40°F.

You should be concerned about the correct charge because at this point, I don't think you know precisely how much refrigerant the system contains. And the charge amount needs to be precise. Also bear in mind that pressures can't tell you that. Weighing-in the exact amount of refrigerant is the only way to charge a system correctly. Your system holds such a small amount of refrigerant that just a slight overcharge or undercharge will negatively affect performance.

At this point, I suggest having the system recovered, and then evacuated and recharged to the manufacturer's specifications by a professional MVAC shop.

The specs that I have for your car are as follows: 15 ounces net weight of R-134a, and 4.0 fluid ounces of PAG-46. If you have an under-hood decal with specs that differ, the decal takes precedence.

Why did you replace the components, did you solvent-flush the rest, and how much oil did you add to the system?

[gabton]

Hello John, thanks for your response.

First, temperature was around 80F and humidity 80% for all my readings.

I did try and run the system for 2 minutes at 1500RPM but as soon as I rev up the engine the compressor starts to short cycle. I can't get it to stabilise because (I assume) that the system shuts off on the low pressure cutoff. In the 1500RPM clip, the low side pressure actually drops to 15-20 psi... When it's hovering at 30 psi the car is idle. Isn't 15-20 psi too low ? Could that be the reason why it's short cycling ?

I get that I should be concerned about the correct charge. I will try to book an appointment. Before doing that though, i'd like to be sure there aren't any other issues with the system... I don't want to end up in the same situation if, for example, the expansion valve is bad. I'm pretty sure at some point I had the right charge when adding freon but it always short cycled. I added some very slowly 5-6 times then got readings at 1500RPM every time I added some. Low side would always go down to 20-15 and even 10 psi and High side usually was around 200 psi until it shuts off for 3 seconds. It was 67F out with very high humidity.

I will need to get vent temp with the windows open.

I replaced the component because the compressor had a failure and sent metal shavings all around the system. I did flush all other parts (Lines and Evaporator). I had 2.7 ounces precharged compressor then added some inside the condenser and some in the line when filling up. I must be around 4 oz. This is another thing, I read online it was around 80ml (2.7OZ) for LHW (which i assume is left hand wheel ?) honda civics. I might have a little less than 4 Oz

[tbirdtbird]

15 oz of 134 is a very small amount and needs to be exact.
Please re-read what John suggested should be done, you yourself will not be able to install the correct amount.

Wonder what kind/brand of flush you used, and did you get it all out after.
How long did you vacuum

[gabton]

I used Brake Cleaner with a flush tool plugged into a compressor. Did 2 passes of brake cleaner then used compressed air to insure most of it was gone. Let it dry overnight and next day pulled a 1:30 vacuum.

[JohnHere]

Could the problem be with the expansion valve even though it's new?

If memory serves, a few different TXV's are available for your car depending on the engine size and model (DX, EX, EX-L LX etc.). Wondering whether you got the right one.

[gabton]

Hello John,

It does seem like there are multiple models for the 2012 Civic. I checked and the OEM reference number for the UAC EX10411C TXV I ordered is 80221-TR0-A02. This OEM part seems to fit my 2012 Civic EX 1.8 when I look it up on TorontoHondaParts. There is also the 80221-SNA-A01 that is supposed to fit my car... Both of them fit the 2012 Civic EX 1.8 Sedan !

Yesterday I tested both the compressor temperature sensor and the high pressure switch. They both seem to be functionning well and not triggering the cycling. From my diagnosis, I really think this is a restriction problem. I can be low on charge or overcharged and low side readings always seem to be too low when maintaining 1500RPM. The compressor cycles as soon as pressure drops under 27 psi. Since there is no low pressure switch on my car (Is there ?) I think it's the temp sensor on the the evap core which senses temps close to freezing then disengage the clutch.

Now, yesterday I ordered another TXV. This time I got a Denso 4752073 (with reference OEM number 80221-SNA-A01). I will be installing this and replacing the dryer desiccant. I will then be adding refrigerant by weight.

I was thinking of flushing the evap again but from my understanding, my readings (low side low and high side normal/high) indicate a restriction between the condenser and the expansion valve. Should I do it anyway ?

Thanks !

[gabton]

Could the problem be with the expansion valve even though it's new?

If memory serves, a few different TXV's are available for your car depending on the engine size and model (DX, EX, EX-L LX etc.). Wondering whether you got the right one.

Actually, if I replace the TXV again, should I replace the desiccant and the o-rings of the fittings I'll split ? Since I already did all this last week

[JohnHere]

Best Practices suggest replacement of both the Receiver/Dryer and o-rings. The desiccant in the R/D captures and retains any moisture that's introduced into the system and can't be rejuvenated. You might be able to re-use the o-rings if they aren't deformed, nicked, or torn. Give them a thin coat of PAG oil or Nylog Blue before installation.

[gabton]

Best Practices suggest replacement of both the Receiver/Dryer and o-rings. The desiccant in the R/D captures and retains any moisture that's introduced into the system and can't be rejuvenated. You might be able to re-use the o-rings if they aren't deformed, nicked, or torn. Give them a thin coat of PAG oil or Nylog Blue before installation.

Ok, so I did exactly that. I replaced the expansion valve with the Denso, replaced o-rings where I disconnected the lines and replaced desiccant. I vacuumed and filled by weight. I still get about the same readings...

1500 RPM
200-210 High
20-25 Low
80f ambient temp

I at my wits ends now to be honest... Do you have any other ideas ?

Thanks !