1993 Honda Accord weak AC after total rebuild

Friendly format provided to inquire about automotive a/c systems.
Archived Forum

Moderators: bohica2xo, Tim, JohnHere, Dougflas, HECAT

Lavarider
Posts: 4
Joined: Mon Jul 27, 2020 5:16 pm

1993 Honda Accord weak AC after total rebuild

Postby Lavarider » Mon Jul 27, 2020 5:33 pm

Hi all, I just completed a total system rebuild for a 1993 Honda Accord that had an AC compressor seize up and throw crud into the rest of the system. I ended up replacing the compressor, condenser, accumulator, evaporator, and txv, as well as pulling all hoses and liberally flushing them to remove any possible remaining contaminants.

System was rebuilt with new Orings and placed under a constant vacuum for 2 hours to evaporate any moisture, then left overnight under vacuum to check seals. Once that passed, it was filled with new refrigerant and managed to achieve 38 degrees F from the vents during filling.

Fast forward to the next day, and the AC is extremely weak. The compressor clutch engages and disengages normally, no problems there, and pressures on the system look great (40 low, 205 high, 85 degrees ambient). The low side line is extremely cold to the touch (not freezing, but very cold) and the high side is hot. However, the system cools very sluggishly, and only pushes cool air at idle. When accelerating, the air does get colder than at idle or normal driving speeds, but not as quickly as one would expect from a healthy system. If running on the freeway, the air will constantly cool down and eventually (around 5-10 minutes) get "cold", but this will start to slope back down to "cool" quickly after transitioning back to normal stop and go driving.

Does anyone have an idea as to why this system is running so poorly or have any suggestions for further tests that I could perform to isolate the problem?

Thanks in advance!
User avatar
JohnHere
Posts: 257
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: 1993 Honda Accord weak AC after total rebuild

Postby JohnHere » Mon Jul 27, 2020 6:59 pm

The high side looks pretty good at 205 PSI, but the low side at 40 PSI correlates to an evaporator temperature of about 45 degrees. So I'm not surprised the cooling performance seems weak. What kind of TXV did you install, aftermarket or OEM? And did you charge it by weight? Was this an original R-12 car that was converted to R-134a?
Lavarider
Posts: 4
Joined: Mon Jul 27, 2020 5:16 pm

Re: 1993 Honda Accord weak AC after total rebuild

Postby Lavarider » Mon Jul 27, 2020 9:18 pm

Hi John, this was an aftermarket TXV (Denso 475-2011). System was charged by weight of refrigerant, 30 ounces of R12 as per factory specification. The system has not been converted to R-134 at this time as the owner of the vehicle still possessed a 30lb cylinder of the original refrigerant.
User avatar
Cusser
Posts: 574
Joined: Sun Apr 24, 2016 6:29 am

Re: 1993 Honda Accord weak AC after total rebuild

Postby Cusser » Tue Jul 28, 2020 7:10 am

Lavarider wrote:The compressor clutch engages and disengages normally, no problems there, and pressures on the system look great (40 low, 205 high, 85 degrees ambient). The low side line is extremely cold to the touch (not freezing, but very cold) and the high side is hot.


I'm wondering if warm or heated air is getting into the cold air flow, from like a flap/door that's not closing off the warmer air somehow. I'd check into that.
User avatar
JohnHere
Posts: 257
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: 1993 Honda Accord weak AC after total rebuild

Postby JohnHere » Tue Jul 28, 2020 7:48 am

Lavarider wrote:Hi John, this was an aftermarket TXV (Denso 475-2011).
Although Denso parts have a reputation for quality, I've seen a few brand-new TXVs act up causing the symptoms you describe. You might already have verified this, but is the sensing bulb firmly attached and well insulated using black sticky tape, and is the equalization line's fitting tight? If so, and the problem persists, you might have a faulty TXV. As already mentioned, you could have a re-heat issue as well caused by disintegrating foam seals on the blend door, especially on a 27-year-old car.
Lavarider wrote:System was charged by weight of refrigerant, 30 ounces of R12 as per factory specification.
That's the same spec I have. You didn't mention oil, but my references say it takes 4.5 ounces of mineral oil.
Lavarider wrote:The system has not been converted to R-134 at this time as the owner of the vehicle still possessed a 30lb cylinder of the original refrigerant.
Lucky owner!
Al9
Posts: 203
Joined: Tue Mar 10, 2020 3:26 am
Location: Southern Europe

Re: 1993 Honda Accord weak AC after total rebuild

Postby Al9 » Tue Jul 28, 2020 8:12 am

Well, i highly doubt that reheat issues go away by themselves once RPM goes up.

Don't know the specs but if it has a 134A-tailored cross-charge this could possibly be the problem. Floods evaporator below a precise evaporator pressure value and the two refrigerants have different P/T charts. Which is another reason as for why converting to R-134A is always the best option IMHO.
User avatar
Tim
Site Admin
Posts: 480
Joined: Tue Apr 12, 2016 2:19 pm
Location: Scottsdale, Arizona
Contact:

Re: 1993 Honda Accord weak AC after total rebuild

Postby Tim » Tue Jul 28, 2020 9:04 am

Listed pressure at idle of 1500 rpm? If idle post readings at 1500.
------------------------------
Please support ACKITS.com for your Auto A/C Parts and Tool needs.
P:602-233-0090
Lavarider
Posts: 4
Joined: Mon Jul 27, 2020 5:16 pm

Re: 1993 Honda Accord weak AC after total rebuild

Postby Lavarider » Tue Jul 28, 2020 12:26 pm

John, I attached the TXV bulb firmly with two metal hose clamps and insulated it with cork tape, but there is no way for me to check at this moment whether the txv is still firmly attached as on this car I would have to break the AC system seal to do so, and would rather not have to do that unless absolutely necessary to diagnose as I don't have personal access to a recovery machine, which would make recovering and repressurizing an R12 system more of a hassle than I'd otherwise want it to be.

AI9, what do you mean when you say 134A-tailored cross charge? The system was originally built for R12, and has been charged with pure R12. It was fully evacuated and flushed before new refrigerant was injected, and oiled with 4.5 ounces of Mineral Oil.

Cusser, the blend door actuator appears to travel fully and the door moves without binding. Switching from cooling to heat with the AC on causes the system to blast absolutely roasting air which doesn't feel like its being made more mild by the presence of AC, so I don't believe the blend door seals are leaking.

Tim, pressures at 1500 RPM were 30 Low 223 High @ 82 degrees F. The system also performed much better during this test cooling wise than at the car's natural idle of 650 rpm.
Al9
Posts: 203
Joined: Tue Mar 10, 2020 3:26 am
Location: Southern Europe

Re: 1993 Honda Accord weak AC after total rebuild

Postby Al9 » Tue Jul 28, 2020 12:41 pm

Lavarider wrote:AI9, what do you mean when you say 134A-tailored cross charge? The system was originally built for R12, and has been charged with pure R12. It was fully evacuated and flushed before new refrigerant was injected, and oiled with 4.5 ounces of Mineral Oil.

The system may use whatever refrigerant, but certain TXVs are filled with a mixture of different gases (a cross charge) that makes the TXV operate with positive superheat (i.e. flow restriction and a resulting suction pressure pull-down action) only down to a certain suction pressure - then the bulb charge pressure abruptly becomes greater than the evaporator pressure and the orifice stops closing, and might even open more. Resulting in a flooded evaporator and a break in the suction pull-down action. This is intended to happen right as the evaporator is about to reach freezing temperatures, since it stops suction pressure from decreasing even further.
I summed up what is stated in patent US4979372A.

Obviously enough, using a valve intended for a certain refrigerant in a system containing a different refrigerant featuring a different P/T chart might create pressure issues and resulting cooling problems. Cross charge valves may further amplify them due to the peculiar way in which they operate.
User avatar
bohica2xo
Posts: 810
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: 1993 Honda Accord weak AC after total rebuild

Postby bohica2xo » Tue Jul 28, 2020 3:18 pm

Lavarider:

Those pressures at 1500 look very good for that system. 30psi on the R12 system is about perfect, 35f suction. The TXV is fine.

You probably have a reheating issue, or air is bypassing the evaporator core. Sometimes when you replace an evaporator core, a foam seal has disintegrated to the point you do not know it was originally there.

The reason we ask for 1500+ rpm testing is to get the compressor speed up to where it can feed the expansion device fully.

Ignore all of A19's noise, he is still learning how all of this stuff works.

The TXV bulb could be full of R22, ammonia, R502... None of that would make any difference as long as the spring in the TXV was calibrated for it. The target Temperature for the sensing bulb is what matters. Besides, the difference in suction pressure at the critical 32 to 35f range is 2 psi between R12 & 134A

Return to “Automotive Air Conditioning Forum”