Is it normal for the AC HPS to fuction often?

[SHOtimer]

It has been 100+ here for the last few days, and my AC high pressure sensor has been getting a workout apparently. It is cutting the AC a lot. If it is hot out and I am driving in town...in stop and go traffic it will every time I accelerate the cut out switch will cut the AC till the pressure drops. Even at higher speeds on the freeway...it will cut the AC. If I drive around 45 (1.5k RPMs) the compressor will stay on and get cool, but if I stop and go with the RPMs moving...the compressor will be cycling so much that it won't really get cold. I just got the system evacted and filled, and it was not overfilled. When the ambient temps go down to the 80's the system will work great, without cycling and get nice and cold.....

Any thoughts as to why this is happening?

Thanx, Doug

 

[rangerj]

Did the shop that evac'd the system and filled it take pressure readings after they filled the system? Is your radiator fan being activated when the A/C is on? How do you know it is the high pressure switch that is cutting off the A/C clutch?

A high pressure build up is commonly caused by inadequate cooling (fan not working) and more commonly by a improperly working oriface. The oriface regulates the flow of the liquid refrigerant into the evaporator. If it lets too much liquid flow through the evaporator will have ice built up on the cooling fins. If there is a blockage at the oriface the heat exchange process is too little to produce cold air, that is there is too little liquid refrigerant getting into the evapoator to evaporate into a gasous state and absorb heat while doing that. These are a few common possibilities.

We would need more information to be more helpful, such as the pressures for the high and low side at (what) ambient temperature, as well as the answers to the questions asked above. Have you tried jumpering the high pressure switch? Do NOT do this until you know that the pressures are in the normal ranges. Maybe the high pressure switch is doing exactly what it is supposed to do, that is protecting your system from excessive pressure.

 

[SHOtimer]

They did take readings, when they did it, it was cooler (when it is cooler the system runs perfect) - he said it was 225 and 35.

I have verified that the fan is always on when the AC is on. And that it runs at both its speeds.

I bought the harbor freight set of AC gauges to use, so I sampled a bit of the pressures. This was a few weeks ago, when the ambient temperature was in the high 90's. When the AC was kicked on I got 325 and 56...after running a bit it went to 300 and 65. I gave it some gas and the pressures went to 450 and 45, then the compressor shut off. Which lead me to believe because of the high pressure side, that it was the HPS shutting down the compressor.

In regards to the fan, it is the original at 180k, when it is on with the hood open it sure is moving a lot of air, enough to lead me to believe it is working properly.

The system currently has a 'VOV' orfice tube in it. This was installed, to hopefully improve the cooling capabilities of the system. Kragen, had the regular orfice tube, and the 'VOV' one. I am wondering if that is a problem - having a non-standard orfice tube in there?

I did no know that I could jumper the HPS, it looked a little more complex than the LPS. I would be willing to try that if I knew how.

Also, when it is cooler out I get ice cold air, and I can't feel the load of the compressor on the motor. When it is hot out and not cooling very well, it creates a huge drag on the motor that I can significantly feel. This also leads me to believe it is a high pressure problem, it just confuses me that it only presents itself as a problem when it is hot out - which of course is when I need it the most.


Doug

 

[projectSHO89]

With pressures like that, you do indeed have a problem.

The list of suspects include:

Overcharged
Orifice/VOV restricted
Condensor restricted.

The blue Ford orifice works quite well.

It is never "normal" for the HPS to operate, it's there as a safety.

Steve

 

[SHOtimer]

With pressures like that, you do indeed have a problem.

The list of suspects include:

Overcharged
Orifice/VOV restricted
Condensor restricted.

The blue Ford orifice works quite well.

It is never "normal" for the HPS to operate, it's there as a safety.

Steve

Ok. I have had the system evacuated and recharged several times by a couple different shops, thinking that maybe the charge had some air in it or that it was overcharged or what not. Everybody has always said the charge was perfect. The Compressor/orfice tube/Dryer all have 10k on them. The only part that has is original to the 180k system is the condenser and the evaporator. The condenser was flushed and pressure checked when I had the system apart, and they said it was fine. I have the stock tranny cooler on the car, and a stacked tranny cooler that is mounted to the condenser, could that be causing a problem?

The odd thing is when ambient temps are around 60s the system works beautifully. Of course, but who needs it when it is that cool.

The car does this on the freeway also, so I assume that - that would disqualify the fans as a problem, because at that point they are out of the equation...correct?

Ok, the 'blue' Ford orfice, is that just the 'motorcraft' replacement orfice tube hose?

So, what should my next step here be? Should I install a different orfice tube? Should I put in a new condenser? With the temps being over 100 I am becoming frustrated with the system to say the least.

Thank you for the help so far guys.

Doug

 

[SHOtimer]

bumpidy bump.

Doug

 

[projectSHO89]

Just noticed it's a 95. Should be an orange (.057"), not blue (.062") orifice tube.... These cost about $2-3 at any parts store assuming you have a liquid line that has a removable o-tube.

What to do depends on how much you want to spend. Since I do my own work instead of paying a shop, I'd replace the o-tube first to see if that fixes it then replace the condensor if it doesn't. You'll have to base your decision on the relative costs of doing it in steps or all at once.

All this assumes that you do not have airflow through the condensor restricted due to dirt, etc.

Steve

 

[SHOtimer]

I also do my own work, except for the evac and recharge. If I am going to open the system I'll just replace the orfice tube and the condenser. It is a bummer to replace an orfice tube that has only been in there for 10k. I hosed out the fins of the condenser when I had it out....so I don't think it is clogged externally.

Does the condenser hold much oil? Should I add any(oil) to a new condenser?

Thanx, Doug

 

[projectSHO89]

For the A/C condenser core (19712), add 30 ml (1 ounce) of clean Motorcraft YN-12b refrigerant oil or equivalent meeting Ford specification WSH-M1C231-B to the A/C condenser core or the suction accumulator/drier if the A/C condenser core is replaced.

This is PAG oil.

FWIW, you can probably buy a pump and guage set off ebay and DIY yourself for what the shop will charge.

Steve

 

[SHOtimer]

Ok - fabulous. I already have a gauge set, I hadn't looked into the pumps, I figured they were probably expensive. I will be poking around ebay.

Thank you for your help, I really appreciate it.

Doug

 

[projectSHO89]

I just ordered a 2 cfm pump for $115 shipped. ebay seller usatoolswarehouse. Ive done previous business with them this year and was very happy with their pricing and service. My new stuff should be here in a few days.

I have been using one of the air-powered pumps but I've given up on it. Won't draw a deep enough vaccum plus its air demand is unbeliveable.

R134a can be bought from my local WalMart for $6.88+tax per 12 oz can. At least $2 per can cheaper than any auto parts store.

Steve