M7040 - AC works but blows hot after a while

[Flintknapper]

You are right, I did not think to detail the procedure I followed for recharging it. It had the hole in the evap when I purchased it, so we can probably assume it was like that long enough to where the system had reached 100% equilibrium with the outside.
Here's what I did (after installing new drier, evap and exp valve):

1. Pulled vacuum, left pump on for for almost 2h while doing this.
2. Turned pump off and closed system down to observe if it would hold negative pressure, waited 1h plus - no change.
3. Filled with nitrogen, and pulled vacuum again, times 4 (I was advised to do this by someone who works with ACs, but I admit I did not look up exactly what this would achieve, I just did it because it sounded like a good idea lol)
4. Finally recharged with the refrigerant, and I also put in a little dye and some PAG oil, which was mostly guesstimated yes. Refrigerant is R134a. 2.09 lbs (I weighed it, and tried to get as close to 2.09 lbs as possible as per tractors stated capacity).

It is definitely possible the compressor is corroded on the inside. In hindsight I wish I would have replaced it as well.

Today I ran it hot and then poured some cold water on the condenser. This had the effect of dropping the output temp from 80 to 60 in just 2-3 minutes. I don't know if this means the compressor is fine, or if it might still be the culprit (or one of the culprits).

Thanks!

IF you used a rented vacuum pump then always replace the oil in the pump for best results removing moisture from the system. Always shut off all valves (manifold gauges and valves at pump) BEFORE shutting down the pump.

If the system held vacuum (28inHg) or better then you were fine. If you purged the lines correctly...then there should not have been any significant amount of air introduced.

Sounds like you charged it correctly. If the compressor were weak or failing it would show as low pressure on both the low and high side.

IF you had a restriction, you would see higher than normal high side pressure and lower than normal low side pressure (even going into vacuum).

As previously mentioned I would turn my attention first to air flow issues. Make sure the fan belt (if belt driven) is tight and not slipping. Make sure all components (Radiator, Condenser, oil coolers) are clean and do not have the fins bent or dirty.

And most importantly.....check the fan shroud to see that air is not escaping around it and the radiator.

 

[DustyRusty]

When cleaning an evaporator or condenser you can't just blow it clean, you have to properly clean it with a detergent. I use Simple Green foaming coil and condenser cleaner. It is available at Home Depot.

 

[btcfarmer]

I was going to make a suggestion, however, all the things that I thought of have already been mentioned. When I do AC work I pull a vacuum for a minimum of 24 hours, and then charge with nitrogen and note the pressures. If it holds the nitrogen for another 24 hours I will charge the system weighing the refrigerant as I install it. Most times I will put 80% of the stated refrigerant into the system, and then run the system watch the gauges, and slowly add refrigerant on the low side until I get the gauge readings that are shown in the service manuals. The only thing I can think of that hasn't been mentioned is whether you wrapped the expansion valve with the black refrigerant cork tape, properly affix the sensing bulb to the evaporator core, and wrapped it with the black refrigerant cork tape. I only work on old car systems using R-12, and that stuff is so expensive that you don't want to make mistakes.

Update: I just read one of your replies, and realized that you only guessed at the proper amount of refrigerant oil. If I were doing that repair, I would have pulled the compressor and drained the oil, flushed the system with a refrigerant flushing agent, and blown it out with compressed nitrogen to make sure that the system was clean of any debris. Working on refrigeration is like a surgeon doing surgery, you have to have a clean environment and clean piping. If the system was open to the atmosphere, you have no idea of what might have gotten into it.

I only pulled vacuum for about 2h, and then waited for just about 1h before beginning the nitrogen cycles. So I did not vacuum-pump or wait anywhere near as long as you. If I end up evacuating and redoing the job, I will follow your routine instead.

I did properly affix the sensing bulb (put it in the same exact way it was inserted in the old evap), but I did not use refrigerant cork tape (on account of me not knowing it was a special type of tape). So it sounds like I should order some of this and fix that mistake.

I did indeed guess the proper amount of refrigerant oil. From what I knew at the time (or thought I knew after watching some youtube videos) this seemed like it would be ok. But maybe not.

The system was open to the atmosphere and it probably had been sitting like that for months.

Thanks for your advise.

 

[btcfarmer]

IF you used a rented vacuum pump then always replace the oil in the pump for best results removing moisture from the system. Always shut off all valves (manifold gauges and valves at pump) BEFORE shutting down the pump.

If the system held vacuum (28inHg) or better then you were fine. If you purged the lines correctly...then there should not have been any significant amount of air introduced.

Sounds like you charged it correctly. If the compressor were weak or failing it would show as low pressure on both the low and high side.

IF you had a restriction, you would see higher than normal high side pressure and lower than normal low side pressure (even going into vacuum).

As previously mentioned I would turn my attention first to air flow issues. Make sure the fan belt (if belt driven) is tight and not slipping. Make sure all components (Radiator, Condenser, oil coolers) are clean and do not have the fins bent or dirty.

And most importantly.....check the fan shroud to see that air is not escaping around it and the radiator.

I purchased the vacuum pump, so it had fresh oil in it. And 10-4 on closing valves before turning pump off.

The system did hold vacuum at 29-30inHg. I am pretty sure I got those things done right. But thinking now I should have left the vacuum pump on a lot longer.

Sounds like my compressor is in good shape.

Will definitely do my best to clean the components tomorrow.

I know some of the fins on the condenser are bent in. Is it a good idea to attempt to straighten them out with a tooth pick or similar?

 

[DustyRusty]

You roll the dice and sometimes you get lucky. I remember my first venture into mobile air conditioning and all the mistakes that I made. I learned from my mistakes and was lucky enough to get properly trained in a United Delco training school for dealership technicians. The one thing that the instructor drilled into us was that you always have time to do the job over again, but it is better to take your time and do it correctly the first time every time. This is why I will evacuate for 24 hours because I am in no rush. I have updated my tools through the years, and I have learned some new "tricks" such as using a micron meter to determine how low you can draw down a system. Below are 2 readings that I got last summer working on a 1969 Cadillac. It was a challenging job since it held 5 pounds of R-12 refrigerant, and I didn't want anything to go wrong because I didn't have a recovery machine available at the time.

 

[#40Fan]

Cooling off the condenser with water shows that it needs more air flow through it.

You'll get it fixed with more cleaning.

Items like this help if you have the room between the radiator, oil cooler and condensor for them to fit. Can use water as well as air.

https://www.amazon.com/Lisle-88500-...25435&sprefix=radiator+cleaner,aps,155&sr=8-8

 

[BAP]

Definitely sounds like your heater control valve is leaking coolant by. Number 1 problem on ALL brands of tractors with AC systems blowing hot air after 30-60 minutes run time. The plastic shut off valve in the cab that controls flow of coolant through the heater leaks a tiny amount and causes the AC to get too hot and stop working properly. Easiest and cheapest fix is to put a shut off valve in the coolant line coming off the engine and keep it shut off unless you want heat. I have put in many of those over the years in many brands of equipment.

 

[lugbolt]

I'm still gonna lean towards compressor based solely on the pressure readings.

the high side, I'd like to see 220-250 on a warm day and then on the low side 25-30 after the cabin cools off. 30-35 with a warm cabin. Remember, pressure and temperature are closely related.

dumping water over the condenser is always going to drop the pressure-and with that, the temperature. Sometimes I thought about putting a washer pump and reservoir on my truck for this very reason.

i wonder if the clutch is failing? It could give similar symptoms of a slipping belt. I've run into this before on an L4240HSTC I think it was.

if the system was open a while, I would imagine that the system has debris in it which would further reiterate a possible compressor failure. Noone knows how long the system was open, and noone knows when/if the system was operated with a hole in it, which would allow the compressor to eat any dirt/dust and moisture. IIRC these don't have a HPCO, which would otherwise keep the compressor from running with zero psi in the system. AND who knows who's charged it, how they did it, and with what, in the past.

Since your low side is high and your high side is low, that would generally be indication of either a weak compressor or an expansion valve that is sticking or not working or maybe slippin belt or clutch, but again without being there it's hard to say for sure.

 

[number two]

Interesting thread!
OP has not posted back.
I'm thinking he found coolant leaking into the heater core was the problem.
He seemed well versed in AC repair!

 

[Tx Jim]

All sorts of "possibles" mentioned, but before changing anything I would pinch off one of the heater hoses and try running like that for a while. See what difference that makes.

I recommend installing manual heater hose cut-off valve & adding some refrigerant while monitoring high side pressure gauge .