Can We Find a Competent AC Tech in Karachi?

[pwuser162557941033]

Yes. He told all sorts of stories.

He unfortunately didn't have the R134a 1/4" SAE lines, only the quick disconnect type, so he couldn't hook up a manifold. But I can check pressures at another closer shop. I don't have a line set either.

The suction and discharge lines near the exhaust are all insulated, one with glass fiber wrap, one with residential AC foam insulating hose.

[pwuser162557941033]

Now see that your compressor pumps up a solid head pressure or not, the txv is the variable choke point which is now functioning so your liquid pressure should be nice and high now.

Oh, you're saying it was basically wide open (or close to that) before and now the high side should show more than the 160 psi we previously had because the TXV is restricting flow appropriately to ensure all the sprayed refrigerant has vaporized by the time it gets to the end of the evap.

1. What should I look for on the pressures? Lower low side, higher high side? The compressor is noisy and Sabir doesn't want to use the Chinese one.
2. Would you say the next step is vacuuming the system and charging it fresh with the correct weight of refrigerant? Or something else?
3. Is there really a difference in R134a cans from USA, China, Malaysia, Thailand, etc. - Sabir is insistent that there is. I'm planning on just buying whatever can of R134a that doesn't look counterfeit.

I know that adulterated/counterfeit gases exist. Lots of fake Genetron cans apparently have R-12 in them instead of R-134a.

[Xulfiqar]

On the vapour side you be seeing about 35-40 psi and about 180-200 on the liquid side.

The vapour side should be like touching an icecube, just a hair above freezing temp after the system has stabilized itself and cabin is cooled down somewhat (close the fresh vent)

Btw, dont keep on attaching manifolds to it, if you do then make sure the tech actually purges his manifold back to your system as liquid gas will be filled in the high side line.

The line purge is possible only with a valve head that can be isolated like a quick connect or a ball valve at an SAE fitting. If you lack both then you will lose that refrigerant in the liquid line, top up will be necessary. (A regular 4 ft line can hold upto 40 grams)

Buy yourself the r12 to r134a adapters from a shop selling car ac parts, ask sabir where to go. Attach them so you have quick connect ports to work with.

Btw did you replace the schrader cores? I do that on every job as its cheap insurance.

[pwuser162557941033]

On the vapour side you be seeing about 35-40 psi and about 180-200 on the liquid side.

Got it. If I don't, I'll start looking at the compressor.

The vapour side should be like touching an icecube, just a hair above freezing temp after the system has stabilized itself and cabin is cooled down somewhat (close the fresh vent)

Yes, and this should be at idle, too, right? Fast idle/driving should trip the evap thermostat and provoke cycling, as I understand it.

Btw, dont keep on attaching manifolds to it, if you do then make sure the tech actually purges his manifold back to your system as liquid gas will be filled in the high side line.

The line purge is possible only with a valve head that can be isolated like a quick connect or a ball valve at an SAE fitting. If you lack both then you will lose that refrigerant in the liquid line, top up will be necessary. (A regular 4 ft line can hold upto 40 grams)

You're absolutely right, this is something AC guys know nothing about, constantly introducing ambient air and letting out refrigerant every time it's done. I allowed this with all the shops above because before I visited them all, I suspected the system was overcharged. I'll make sure to recharge by weight when I do it.

Buy yourself the r12 to r134a adapters from a shop selling car ac parts, ask sabir where to go. Attach them so you have quick connect ports to work with.

These are available online, too. I'll ask Sabir for the place to get them also.

Btw did you replace the schrader cores? I do that on every job as its cheap insurance.

On the service ports? No, apparently even those are "jaali" these days, and everyone keeps the genjan items. I'll ask Sabir about this as well.

---

Shopping list:

• Vacuum Pump
• R134a 1/4" SAE Hose Set for Manifold
• R12 To R134a Quick Disconnect Service Port Conversion Kit
• Weight Scale (meat shop type won't have a power-off timeout and will update faster)

[Xulfiqar]

Btw

For r134a in Pakistan, there are a lot of issues. Some peeps are selling the little coke cans of them filled at a production line, most ac shops are buying r134a filled in recycled 30lb containers without vacuuming.

This is a big problem, you are adding pre adulterated refrigerant, couple that with a hit or miss vacuuming and you just lost quite a lot of performance right there.

[Xulfiqar]

Btw

Scales are cheap now and excellent to use to measure battery electrolyte sg too. Makes it simpler and provides you with dead accurate measurement rather than the stupid wax float tube.

[pwuser162557941033]

most ac shops are buying r134a filled in recycled 30lb containers without vacuuming.

I found this out when I learned it was being done to R-32 and R-410a cylinders. When I was looking for techs for my home air conditioner, most of the "two dudes on a motorcycle with two cylinders on either side" gangs had refilled cylinders. On the auto side I've seen plenty of proud "USA gas" users that have blatantly counterfeit packaging and cylinder labels.

This reinforces using cans for me as well.

[pwuser162557941033]

Now see that your compressor pumps up a solid head pressure or not, the txv is the variable choke point which is now functioning so your liquid pressure should be nice and high now.

Here's the system pressures after charging about 100g of refrigerant. No vacuum pump yet, just topping up. A lot is vented while screwing into the R-12 service ports.

And here it is running at idle 15 minutes later, same charge.

The liquid side drops and the vapor side rises as the compressor heat soaks, it seems.

[Xulfiqar]

Pressures look good, the reason you are dropping liquid pressure is the txv is opened up, probably due to the condenser heat soaking and the evap temp raised too.

Is the suction line sweating? What happens at fast idle like at 2000 rpm?

You had an ntc at the evap outlet after the txv, what does it read?

Use that to calculate the superheat of the system, you have a gauge with the evaporating pressure readout,

I see 48 psi which is 12c, if your evap is at 18c you have 6 degrees superheat, which seems okayish, but on txv system the superheat is managed by the txv, you need to measure subcool at the liquid line

Same characteristics and values, condensing pressure temperature and actual temperature of the line will tell you subcool, you should be close to 2-5c - this best done at fast idle with a cover on the windscreen and vent closed off.

[pwuser162557941033]

Suction line and evap are both sweating, yes.

Gave myself some nasty frostbite wrangling the cheap fittings in the dark, venting a lot of refrigerant. Will order the quick disconnect conversion adapters. Didn't precisely check fast idle, will do again later.

Attached another NTC to the line exiting the dryer, just after the liquid service port.

Here's the current state after the huge loss of refrigerant - AC on, full fan speed, recirc is always on in this car, and it's nighttime now:

Evap out line temp 13°C
Discharge line temp 39°C

[Xulfiqar]

At 41psi evaporating pressure you get 8c, in real measured you see 13c, so about 5c superheat.

Looks good here and on subcool too at 5 degrees.

Now find some aluminum cladding insulation for the suction line and make sure to have an airgap in it too so it doesnt corrode it away.

Drive the car and see what it does in daytime. Make sure your condenser fan(s) is good and not installed lazily.

Dont jump to conclusions very quick on these systems as the hysteresis is rather weird on these txvs. Let it work and stabilize for a bit then retest.

[pwuser162557941033]

At 41psi evaporating pressure you get 8c, in real measured you see 13c, so about 5c superheat.

Looks good here and on subcool too at 5 degrees.

That's good to hear, thank you. I was still looking at the PT charts, it's right there on the gauge.

Dont jump to conclusions very quick on these systems as the hysteresis is rather weird on these txvs. Let it work and stabilize for a bit then retest.

Observing the system with the charge level from earlier in the day, I saw the evap temp quite steadily oscillate from 22C to 19.9C. Fast idle would get it colder fast, letting throttle go would have it go back up to like 24C. It does behave strangely.

Now that I have less charge than this afternoon, and the superheat/subcool values check out okay, I'll observe how it performs during the day. Do you think whatever level of charge we're at now is correct based on the superheat/subcool? Of course, only vacuuming down and recharging by weight will tell a complete story.

Drive the car and see what it does in daytime. Make sure your condenser fan(s) is good and not installed lazily.

It's the stock fan, it's probably worn out by now. Attached with zipties and has foam sealing it to the condenser. I don't think I could get something like a 12V Spal fan, so I'll see what options I have. The fan setup is as follows:

Front of the car
↓
Condenser fan (pusher, shrouded)
Condenser
↓
Air gap (foam strips on the top and sides)
↓
Radiator
Radiator Fan (puller, shrouded)
↓
Crank Pulley

Here's what the condenser fan looks like, Suzuki P/N 95320-55X51, 12V 77W rated.

Now find some aluminum cladding insulation for the suction line and make sure to have an airgap in it too so it doesnt corrode it away.

Here's what it looks like right now. Arrows are the insulated suction line.

Could I get away with aluminium foil on top of the thick foam insulation hose just to see what effect it has? The insulation hose covers the suction line throughout and goes all the way to the bulkhead.

[Xulfiqar]

Insulation looks fine, that POS condenser fan is trash. And if you have a serp condenser its even worse.

Find a replacement, btw is your engine fan clutched or fixed?

Btw, yeah

The gauge has the temp printed on it, the nicer digital manifolds display the sub cool and superheat for you on the same screen.

[pwuser162557941033]

Yeah, the blade distribution and design didn't make any sense to me either. I'll try and find some kind of pusher fan. There's Chinese ones available online for <$50-60, not sure about their performance.

It used to have a clutched fan long ago that seized solid, now it's an electric radiator fan from a PKDM Alto. I only think the rad fan is okay because it immediately drops coolant and oil temps as soon as it turns on. Right now, I have both fans running constantly with the compressor, all the gauge readings are with both fans running.

The gauge has the temp printed on it, the nicer digital manifolds display the sub cool and superheat for you on the same screen.

This is what I was trying to tell Sabir with his new Alibaba digital manifold he insisted was "from USA" - the saturation temps are right there referenced from an internal lookup table for the selected refrigerant, and if you buy the two clamp-on temp probes, they plug in and calculate superheat/subcool live for you right there.

He only had it for bragging rights, not to actually read what's on the screen, unfortunately. I got to see everyone using it around the shop with the low side only.

POS condenser fan is trash.

Is it so bad that it's just causing a restriction sitting there, running or not? I could remove it and see how it affects performance. It sits between the front grill and the condenser, which would otherwise have access to fresh air.

BTW saw this at a shop for sale for ~$60. Should I get it? Or try and get a used multistage?

[Xulfiqar]

Too bad that hes devolved into the brag wagon, but a while back he was more focussed on quality delivery and less on brag.

Anyway, you now have more ammo than most shops in pk to solve automotive ac issues.

Btw, any given time a fan is called for in a car, a puller is always preferred unless your pusher is twinned or has some other issue,

E.g. on clutched fan engines, the weaksauce pusher fans job is to push air so the fan clutch can warm up quicker and lock, the fan clutch then takes over as it can blow a tornado of air,

On electric puller fan cars, dont use a pusher it creates a block for air flow. And on your puller make sure the shroud is sealed to the edges of the radiator/heat exchanger to get maximum airflow.

[pwuser162557941033]

On electric puller fan cars, dont use a pusher it creates a block for air flow. And on your puller make sure the shroud is sealed to the edges of the radiator/heat exchanger to get maximum airflow.

Okay, I'll get rid of the condenser fan. So one puller behind the radiator should be enough for the condenser too?

Yes, every shroud is sealed to the gills with foam and a little bit of adhesive.

[Xulfiqar]

Good
Is the shroud covering the whole surface area?

Btw, friendly advice, eye shield and gloves please, frostbite is a bastard!

[Xulfiqar]

Used multistage would be best if its not literal garbage, however this one will suffice and be much better than “frijj ka komressor”

[pwuser162557941033]

A few millimeters exposed, but otherwise yes.

Side profile of the condenser/rad sandwich.

[pwuser162557941033]

Btw, friendly advice, eye shield and gloves please, frostbite is a bastard!

Absolutely. I work with my hands for a living too, albeit in a very different discipline. Electrical workman's gloves I'm assuming, or just nitrile/latex ones? Leather gloves. The oil exposure along with the cold makes it particularly important and really nasty.