Ford Econoline:


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# 1  7/6/2013 9:15 PM

New member
Registered: 7/6/2013
Posts: 1


When I accelerate the A/C stops blowing cold air. The blower still works . when I ease off the gas the clod air comes back. I recharged with Freon but I get the same Result. Could I have a vacuum Leak? any input would be appreciated I drive a E-250 2004 4.9 litre



# 2  7/7/2013 3:19 AM

Registered: 11/24/2009
Posts: 1299

Re: A/C

There are two pressure switches in the A/C system; a low pressure switch and a high pressure switch.

When the compressor clutch engages and the system is operating normally; the clutch will disengage when the pressure on the low side is to low (usually 22 to 24psi) when the pressure is above that range it will close it's contacts inside the switch which will allow the compressor to engage again. This can also be referred to as the cycling switch. This helps prevent the evaporator from freezing up and block air flow going through the evaporator by cycling the compressor clutch on an off. This keeps the evaporator just above the freezing point so it won't accumulate ice on the evaporator.

The high pressure switch opens the clutch circuit when the pressure gets too high on the high side of the A/C system which could cause compressor damage usually from a blockage in the A/C system,

I would guess there is probably not enough Freon in the system because I don't know if you have an Auxiliary climate control or regular climate control.

Installing pressure gauges before the engine is running and then check the pressures while the engine is running and compressor engaged can help determine which switch is shutting off the compressor clutch on acceleration. If it appears the low pressure (cycling switch) is disengaging the clutch too early then you would probably need to add a little more Freon.

I listed the specs for fluids and pressures for the A/C system from the Alldata Automotive information website below.

Pressure Cutoff Switch:

Open status 2,999-3,275 kPa (435-475 psi)
Closed status 1,586-1,999 kPa (230-290 psi)

A/C Cycling Switch Open and Closed Pressures:

Open pressure 152-165 kPa (22-24 psi) 
Closed pressure 317 kPa (46 psi) maximum

Refrigerant Lubricant and Capacity:

Capacity without auxiliary climate control 266 ml (9 oz)
Capacity with auxiliary climate control 384 ml (13 oz)

Refrigerant and Capacity:

Capacity without auxiliary climate control 1.13 kg (40 oz) 
Capacity with auxiliary climate control 1.70 kg (60 oz)
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