AC Not Engaging Warm Air (1 Viewer)

[FranceJohnson]

I have read through several threads on here about different issues of AC problems. Didn't find one that answered my question. I have a 99 LX470 with 288k, the AC worked fine last summer, but is now just blowing warm air, front and rear.

The AC switch lights up, and stays illuminated (does not blink). I checked the low side pressure and it is in the green range (with compressor off). On both AUTO mode and manual when the AC is turned on, nothing changes in the engine. The AC clutch doesn't engage, and the fan doesn't turn on.
I assume like most engines, when the AC clutch engages there should be a slightly larger engine load (audible), and the electric fan should engage. I gave the clutch a couple bumps thinking it might just be a little sticky, but no change.

So, given that this truck has 288k and we live in a desert; I have no issue replacing the AC compressor...if that is the problem.

Can someone give me some pointers on how to isolate where the issue is coming from. Here are the issues I have read about:

Blown Fuse-easy, straight forward, first place to look.

Bad Relay- (would the switch illuminate if this is bad? or blink?)

Cabin Temp Sensor- If the front is warm but rear is cold.

Blend Door- AC clutch engaged, but blowing hot air.

Bad AC amplifier-will not engage the clutch, assuming it does not have a reading for the RPMs.

Bad AC Compressor/Clutch- if the clutch fails, and it doesn't engage; will it not trigger the fan as well?


So, starting with blown fuses which are easy to check, and eliminating Blend Door and Cabin Sensor, since they do not fit my symptoms; what is the best way to isolate a bad relay, from a bad AC Amplifier, from a bad Compressor Clutch?

Is there another relay on the vehicle that can be poached? Can the A/C amplifier be bypassed? I found a new DENSO ac unit for $200 which I plan on installing, but I don't want to find out after that it wasn't the problem. I unfortunately do not have an FSM for a 100 series, so if anyone wants to send me one or post up some pages from it, that would be a huge help. I appreciate any assistance.

 

[FranceJohnson]

A little follow up to this. I was able to track down a PDF of the FSM and review the ac section. I had ordered a new Denso AC compressor and installed it along with pretty much all the moving parts and seals on the front of the engine during the 3rd 90K service. The valve covers had a slow leak for likely many years, and the AC compressor was pretty well coated. It seemed like a good time to replace it.

I had checked the R-134a level previously using one of the crappy screw on gauges that you buy at Autozone and it registered in the "Green Zone"; but before removing the compressor I went to drain the system and found out that it was completely empty. So, after pulling it back together, and replacing the o-rings of all the AC parts I took off, it would still not hold a vacuum. So, we put a small amount of R-134a into the system and used the "sniffer" to find the leak. We traced the leak to the firewall where it goes to the front evaporator. Replacing the 4 o-rings under the coupler clasps did not remedy the situation. So, the next step is to replace the evaporator and expansion valve. I have read some threads on this and it seems like the housing can fill with debris, collect moisture, and ultimately corrode the evaporator.

I purchased a new OEM Denso compressor for $200 (amazon), compressor oil was maybe $7. I was able to purchase a Spector evaporator, expansion valve, and complete o-ring kit for around $100. Normally I do not like to throw parts at something without knowing exactly what the issue is, but given the mileage and age of all these parts, I feel it is worth it to just give everything a refresh.

AC system previously made me pretty nervous, but after getting into it, I would say once the system is empty, it is worth replacing as many o-rings as possible. A complete kit was about $11, and through it can be a little tedious, they really are not too hard. I plan to pull the evaporator by cutting the glovebox brace, and hopefully clean out the housing a drain thoroughly while I am in there.

Additionally, I checked the rear AC evaporator lines. Common failure place due to rock damage, but everything appeared to be in good shape. Hardest part of this whole thing was removing the rear AC bolt. Everything else is pretty straight forward.

 

[FranceJohnson]

Figured I would post up the resolution to this. After putting everything back together, I could not get the system to hold vacuum. After some frustration, I put enough R134a into the system to kick on the compressor. A gyser of mist/oil/refrigerant shot out of the rear ac liquid line. The failure was in the common area, behind the shield where all the road debris gets trapped.

Ordered a replacement from the dealer which was about $100. As others have done, I put copper RTV around the exposed parts and wrapped them in electrical tape. Replaced the orings on both ends. Install isn't bad, but does require dropping the exhaust. We opted to just throw a new Bosal muffler in there.

All back together, vacuum dawn and held, and refilled. Working great. Spent a lot more time and money on this project but now everything is basically new and ready for the next 17 years.

 

[FranceJohnson]

This AC saga is unfortunately not over yet. The temperature has risen recently and now the system is acting up. To re-cap, I have changed the following:
Denso AC Compressor
Spectra Front Evaporator
Expansion Valve
AC Drier
Rear AC Liquid Line
Most of the O-Rings

The system holds a really good vacuum, and I am confident there are no leaks. The AC systems seems to cycle on these 30-60 cycles of getting cold, and warm. It gets pretty cool, but not really ice cold as I would expect, especially on a 70 degree day. It blows cool for about 15 seconds, then slowly warms back up to ambient. The cycle seems to continue like this. Doesn't really seem to be changed by speed or RPM.

The high pressure side is way way too high, it spikes up to around 300 psi. The low side is maybe 40; both seem to rise and fall with the compressor. One thing that was frustrating when I installed the compressor was the FSM instructions for the AC compressor. I wanted to add the proper amount of oil, but the FSM says, to pour the oil out of the old compressor and measure it. Then pour out the oil from the new compressor, then pour back in whatever amount of oil was in the old one. Issue is, how the heck do you know that the old oil level is correct? This truck is 17 years old and just under 300K now. Who knows how much oil may have been lost, or gained from recharges. I had expected there to be a flat amount to add/confirm for the system. Also, during the refill, it only look about 3.5 (8oz) cans before the system was "filled" per the gauge. Way less than the amount I would expect it to take to actually recharge the system.

So, I am working under the theory that there is just too much oil in the system. I am dreading the thought of removing the AC compressor again to drain the oil out. I have read that an obstruction can cause high-high side pressure. But, coupled with the low amount of R-134a which the system would accept, it would make sense if the oil was taking up too much space.

 

[TXSunDevil]

It sounds to me like you may have an obstruction in the high side. What does your low side pressure read when you high side is up to 300psi? When it is running grab both sides of the AC drier and see if you feel a significant temperature difference to indicate an obstruction.

 

[flintknapper]

This AC saga is unfortunately not over yet. The temperature has risen recently and now the system is acting up. To re-cap, I have changed the following:
Denso AC Compressor
Spectra Front Evaporator
Expansion Valve
AC Drier
Rear AC Liquid Line
Most of the O-Rings

The system holds a really good vacuum, and I am confident there are no leaks.
What are you using to pull a vacuum? Are you getting (and holding) at least 28 inHg? Is the system holding the vacuum for at least 30 minutes?


The AC systems seems to cycle on these 30-60 cycles of getting cold, and warm. It gets pretty cool, but not really ice cold as I would expect, especially on a 70 degree day. It blows cool for about 15 seconds, then slowly warms back up to ambient. The cycle seems to continue like this. Doesn't really seem to be changed by speed or RPM.

With an ambient temperature of 70° F. you should easily have 40° vent temps. The cycling issue is likely related to the refrigerant charge (IF you indeed have no leaks...which I am not convinced).

The high pressure side is way way too high, it spikes up to around 300 psi. The low side is maybe 40; both seem to rise and fall with the compressor.

High side pressure as you noted is WAY too high for an ambient temp of 70° F. The low side is on the high end of normal, but also high (in my estimation) for that ambient. IF the low side was fairly constant and the high side 'high' (neither fluctuating very much) I'd say you still have air/moisture in your system and possibly too much oil.


One thing that was frustrating when I installed the compressor was the FSM instructions for the AC compressor. I wanted to add the proper amount of oil, but the FSM says, to pour the oil out of the old compressor and measure it. Then pour out the oil from the new compressor, then pour back in whatever amount of oil was in the old one. Issue is, how the heck do you know that the old oil level is correct? This truck is 17 years old and just under 300K now. Who knows how much oil may have been lost, or gained from recharges.

Yes, those instructions MIGHT work for you if you were stuck somewhere out in BFE and had no other way to properly charge the system with oil. Not only does it not account for oil lost due to leaks or prior evacuations, it doesn't consider the amount of oil still present in the evaporator, drier and condenser (not large amounts, but its there). Your system should take 7.75 ounces (AFTER the system has been evacuated and flushed to remove remaining oil and debris). Too much oil will have a decidedly negative effect on the cooling potential of the system.


I had expected there to be a flat amount to add/confirm for the system.

And there IS. BUT it relates to a completely evacuated system. For oil it is 7.75 ounces (even 8 wouldn't hurt). That is for the entire system (including the compressor). If you don't flush the system then its strictly a 'crap shoot' as to how much oil you have in the system. Specs are listed on a sticker under your hood (next to radiator).

Also, during the refill, it only look about 3.5 (8oz) cans before the system was "filled" per the gauge. Way less than the amount I would expect it to take to actually recharge the system.

Your system should take between a minimum of 35.30 ounces and a maximum of 38.80 ounces of R-134a. The 'best' way to properly charge an evacuated system is to weigh it in....and not go by the gauge readings alone.

So, I am working under the theory that there is just too much oil in the system.

Quite possible. If you are overcharged with oil (significantly) and undercharged with refrigerant you definitely will have poor cooling and higher than normal gauge readings.

I am dreading the thought of removing the AC compressor again to drain the oil out. I have read that an obstruction can cause high-high side pressure. But, coupled with the low amount of R-134a which the system would accept, it would make sense if the oil was taking up too much space.

You might have an obstruction...since you did not flush the system. If it were me (especially since you've invested in so many new parts and your time) I'd flush all the lines, the condenser and evaporator (remove expansion valve from evaporator), blow it all out until you are certain the system is dry and clean.

Then...I'd replace EVERY O-Ring you can reach and get a bottle of 'Nylog' and USE IT, that way we know you don't have leaks.

Add small amounts of oil (1/2 oz. or so) to the evaporator, condenser and drier (new drier), and the rest to your compressor.

Pull a DEEP vacuum on the system, check for leaks (system holds vacuum for at least 30 minutes). If the system holds, liquid charge the first can into vacuum at the high side (engine off). HAND turn the compressor (belt off) 8-10 revolutions to distribute some of the oil though the compressor. Reinstall belt, charge the rest of the refrigerant (engine now running) into the suction/low side as a vapor.

We will assume you know which valves on the manifold set to have either open or closed for this process? If not...take it to an A/C shop and let them do it.

See OP's post above ^^^^^^^^^^ Expand.

 

[Stricmic000]

Resolution?

 

[jerryb]

this OP has been spying on me, likely sitting in my garage.

And a question, what does it mean if when you take off the high and low side AC lines off the compressor and a fairly large amount of compressor oil runs out of the low pressure line, where the muffler is? At least a few ounces.
Is that significant?