hi, working on a 1997 F250 5.4L A/C.

When the indash temperature control switch is turn-on to "A/C MAX", after 5 minutes,is blowing hot air instead.

I have jumped both "A/C Pressure Switches", 1 located on the A/C Accumulator and other on in-line high pressure line (looks like a stem value with cap) connected to A/C Condenser.

Directly connect wires from 12V car battery to A/C clutch coil, it turns-on. Before, it would not turn-on. I though the clutch coil was bad but it is not the case.

I let the A/C "ON" for 5-10 minutes, still "NO" cold air, but blowing hot air instead.

I have not check the A/C line pressure with a guage.

From the A/C compressor, the low-side line is not cold and the high-side line is hot. I have compared this to 2006 Dodge Durango Hemi 5.7L which the low-side line is "COLD" and the high-side line is hot.

Could this be the A/C compressor went OUT, need tobe replace?

 

Low side should be cold when its working. If you jumped the switches and still cant get the compressor to turn on, look at power supply to it, ie relays and fuses.
By jumping the switches you defeated its safety mechanisms. With low refrigerant it is not supposed to come on, there is not enough refrigerant to carry the oil and the compressor will self destruct. That is the purpose of the low pressure switch. The high pressure switch also protects, but in another way. If the pressure is too high, such as too much refrigerant for example, the compressor can get "slugged" with liguid refrigerant. In a working system, the compressor only sees refrigerant as a gas. Liquids "wash" the oil out of the compressor, and destroy it too. Liquids don't compress, gas does.

On the flip side though, what happened when you hooked the other battery up to the compressor? Cold then or not...

 

Thanks for the reply, jyount.

The A/C was working fine, blowing cold air last month, May 2011 when I change motor oil and check other fiuld level.

The A/C just stop working 2 weeks ago. Thats when I notice it was just blowing hot air from the dash vents.

Before I jumpered the pressure switches, I notice the A/C clutch would not spin and the low-side pressure was not cold. It spins when I connected two wires from the 12V battery. I let the A/C clutch spin for 5-10 mins., still the low-side preesure is not cold.

The fuses and relay are OK. I test the fuse with digital mutimeter for continuity and for the relays, I swipe out with same rated specific relay with in the fuse box panel. No change with the A/C before I connected directly with with 2 wires from the battery.

Would this mean the A/C compressor need tobe replace?

Just going to the process of limitation before I invest in new compressor. I'm just a shade tree mechanic, when my vehicle needs attention.

 

jyount,

This is the original A/C compressor on 1997 F250 5.4L Triton with 226K+ miles. Never had problems with the A/C before.

 

From what I'm reading here, it sounds like you may be low on refrigerant. the presure switches are doing what they are supposed to.

Make sure you have the proper charge of refrigerant.

Look at the line connections and sevice ports for signs of Oil/dirt. This means that the refrigrerant has been leaking (even if it did work last month).

I would not condem a compresor yet, they are usualy prity durable.

Somewhere under the hood there should be a sticker that should tell you how much refrigerant you should have.

If you have or can get a set of gauges, (with the hand vaves closed and RPM around 2000) you should read about 45 PSI on the low side and about 275-350 on the high side, (dependent on the outside tem.)

With the engine off both gauges should be almost equal and also equal to abient temperature. This means you have a good charge

If the numbert are low you will need check for leaks, you system is low.

If the numbers are high, you may have too much refrigerant, oil or air in the system.

 

Get the gauges on there first.

Also, see the FAQs in the HVAC section of this forum.

 

I would recommend that you take it to a shop and get a basic service. If you try to do this yourself without the proper knowledge and tools, it will cost you a lot more than you could save.

 

Always check the refrigerent charge first. If the system gets below 30psi on the low side it will disengage the clutch. Sounds like you have a leak in the system. Most common issue is the drive shaft for the compressor. This is fixed by replacing the compressor. I would get a DIY can of 134a with leak detector in it. This is a small investment to troubleshoot the system. You will need a UV light to see it. Be aware that system pressure on the low side is depentant on ambient temp. Full charge at 90 degrees is about 45 PSI low side and 220 to 250 on the high side.
Something else to check is the high pressure relief, mine failed and I lost AC in one day. 15 min to change but required the entire system to be evacuated before recharge.

 

If your leak is on the low side and you bypassed out the low pressure switch, you could have very easily pulled non condensibles into the system. That would explain your high discharge temperatures from the compressor. Get it professionally serviced.