Poor cooling - diagnosing weak compressor or a TXV

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PromiseRing
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Poor cooling - diagnosing weak compressor or a TXV

Post by PromiseRing »

-2000 Toyota 4Runner
-200k miles
-91F ambient
-Low side: 42psi
-High side: 220psi
-Vent temp: ~65F

Hello everyone, I am getting 60-70F vent temps on my 4runner. The system was evacuated, vacuumed, and charged by weight. Pressures are 42psi/220psi at 1500rpm. Condenser is clean, fan clutch is GOOD, airflow over the evap is presumably good. Misting the condenser drops pressures to 22psi/120psi, vent temps barely move. I suspected a leaking heater control valve may be trying to heat and cool simultaneously, but I tested the AC on a cooler cloudy day upon a COLD start, and had the same results (before coolant was warmed up).

To me, I have sufficient delta T across the condenser core. I can get those readings later on. Misting it did not make a change in vent temp. I suspect that I might have an issue with the TXV, or perhaps a weak compressor. Is there a way to test each component to know for sure; can a compressor make sufficient high side pressures but lack pumping capacity at the same time?

Comparatively, my brother has the exact same vehicle as me, and gets a consistent 45F vent temp at 1500rpm. Probably closer to 40F while driving. I will note though that his system appears to be a little low on charge because the low side was pulling to 5-15psi during our test, and even cycled the low pressure cut out switch which I thought was somewhat odd on a TXV system.

If I am leaving out any pertinent information, please let me know and I will report back :D
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Cusser
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by Cusser »

Wait for a professional to respond - I am NOT one - but sounds to me like could be low refrigerant level AND poor condenser cooling (either electric fan or fans, or bad fan clutch, or crud on the surface of the condenser). Are ALL the cooling shrouds for the engine in place????
PromiseRing
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by PromiseRing »

I just tested again today, here are my results.

80F ambient, 89psi static, windows down, 1500 rpm, recirc, 29-32psi low, 177psi high. Vent temps at 45F. Much better, but still would like to see 38-42F with ambient only being 80F.

So it looks like today its working rather well. What sorts of things would cause an elevated low side pressure of 42psi on a warmer day?
DetroitAC
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by DetroitAC »

In those same conditions, what is the temperature of the suction line close to the low side service port, give us all the temps and pressures
tbirdtbird
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by tbirdtbird »

While you are at it, also use your IR temp gun and take the temp of the pipe into and out of the condenser and post.

How do you know the fan clutch is good? The viscous fluid wears out after about 3 yrs

Your brother's car is undercharged....an undercharge can fool you because you will get slightly lower vent temps, but this is not good because you don't have enough mass flow of refrigerant and oil back to the comp to keep it healthy. 5-15 psi low is NOT healthy, he needs to check his system before he burns up the comp.

An undercharge is responsible statistically for more than 65% of AC problems
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PromiseRing
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by PromiseRing »

DetroitAC wrote: Wed Aug 10, 2022 5:10 pm In those same conditions, what is the temperature of the suction line close to the low side service port, give us all the temps and pressures
I'm going to be purchasing a thermocouple soon so I can reliably take line temps. If you guys have any recommendations on one I would greatly appreciate it :mrgreen: Today, it was 'beer can cold' when I first started it, but I notice that on hotter days (95F), it sweats a TON and is definitely cold, but not nearly to the extent that it should be.
While you are at it, also use your IR temp gun and take the temp of the pipe into and out of the condenser and post.

How do you know the fan clutch is good? The viscous fluid wears out after about 3 yrs

Your brother's car is undercharged....an undercharge can fool you because you will get slightly lower vent temps, but this is not good because you don't have enough mass flow of refrigerant and oil back to the comp to keep it healthy. 5-15 psi low is NOT healthy, he needs to check his system before he burns up the comp.

An undercharge is responsible statistically for more than 65% of AC problems
Will do. Fan clutch is good, 6 month old genuine toyota fan clutch. Moves tons of air.

I will get those condenser readouts tomorrow. Is there a general rule of thumb for delta T on the condenser?

Ditto on my brothers truck. I had actually messaged him tonight telling him that we need to get the proper charge level in there as soon as possible.

Thanks for the replies
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JohnHere
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by JohnHere »

If on your first test you're reading 42 PSI on the low side (~48°F evaporator temperature, and ~63°F vent temperature), I too, doubt that the hot-water valve is to blame. Toyota valves of that vintage are pretty robust.

Your second set of low-side pressures is much better, but the vent temp of 45°F should be a bit lower based on them.

Could be that the TXV is intermittently malfunctioning.

With 200,000 miles on it, the compressor (if it's the original) might be getting "tired" as well.
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PromiseRing
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by PromiseRing »

JohnHere wrote: Wed Aug 10, 2022 6:44 pm If on your first test you're reading 42 PSI on the low side (~48°F evaporator temperature, and ~63°F vent temperature), I too, doubt that the hot-water valve is to blame. Toyota valves of that vintage are pretty robust.

Your second set of low-side pressures is much better, but the vent temp of 45°F should be a bit lower based on them.

Could be that the TXV is intermittently malfunctioning.

With 200,000 miles on it, the compressor (if it's the original) might be getting "tired" as well.
I just received my Denso TXV in the mail today, but was apprehensive to open up the system to replace it before posting here for a second opinion.

A tired compressor is also a suspicion of mine. I was/am unsure of a way of testing that the pump is pumping how it should, short of replacing it and retesting. Though at only ~$200 for a Denso replacement, I may replacing it next season. Along with a new R/D of course.

Just for fun, what would the symptoms of an over feeding 'partially stuck open' TXV be? In my mind, I would expect somewhat high low side, and somewhat low high side. Kind of how I assume a FOT that is too large would function. Along with a general lack of cooling.
tbirdtbird
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by tbirdtbird »

" I would expect somewhat high low side, and somewhat low high side." Agree, but anything intermittent is problematic to diagnose.
Any air-cooled heat exchanger should be able to obtain a 25-30F spread (your radiator is another example, as is the condenser of your HVAC on your residence.

With 200K on your comp, you are on borrowed time. In this shop we consider anything over 100K to be flirting with catastrophic failure (grenading) thus causing many $$$$ worth of replacing components from the firewall forward. If you plan on keeping the car, or have it be worth anything if you plan to sell, think about replacing sooner rather than later. Do yourself a favor and price out your parts from Tim, the board owner, and owner of AMA (Arizona Mobile Air) at ACkits.com. His quality is good and prices are very competitive.

We changed out the comp on my nephews Lexus a couple of years ago as he had hit the 120K mark. The inside of all the pipes and hoses were squeaky clean. Replacing and flushing all that stuff is a royal pain if it lets go

Are you able to get a thermometer to get accurate vent temps....the digital ones are nice, and there is an analog type with a round dial and a stem
When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com
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JohnHere
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Re: Poor cooling - diagnosing weak compressor or a TXV

Post by JohnHere »

Glad to learn you got an OEM Denso TXV. Some of the aftermarket valves have proven to be problematic over the last few years.

I would replace the compressor now. If you wait, not only will you have to recover, evacuate, and recharge it again but also replace the R/D, which should be changed every time you open the system.

There's no real way to tell whether the compressor is weak other than the pressures. High mileage is subjective but certainly a concern. Even if you take it apart, you probably won't be able to identify, say, a faulty reed valve or an out-of-specs piston. It's best at this point to just replace it.
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