using denso compressor with factory air

[sspence]

I'm doing a LM7 engine swap into my 77 C10 with factory air. I'm ignorant to the ins and outs of A/C so I just assumed all I would have to do is get some hoses made to mate the old with the new. Are there other issues that I'm going to have to address?

[VileZambonie]

The refrigerant is R134A so you will need retrofit fittings. Are you setting it up as a CCOT system or are using the factory PCM and controls from the donor vehicle? What year is the donor?

[sspence]

The motor is out of a 2004 Tahoe. I was planning on using the factory PCM. The truck had been converted to R134 when I bought it. I assumed that whatever signal controlled the compressor on the '77 would control the compressor on the new motor. Is it not just a 12v signal to engage the compressor? Like I said I'm ignorant to A/C systems.

[ehjorten]

The Denso compressor is a fixed displacement compressor and is a CCOT system already.  Computer control of the compressor doesn't really control the A/C so much as it will command electric fans to turn on or off, provides diagnostic trouble codes for the A/C system, and will turn off the compressor under certain engine operating conditions.

[VileZambonie]

On an 04 Tahoe they had dual climate zones, auxiliary units, an HVAC module, automatic or manual controls and so on. The simplest setup would be to adapt it to the trucks controls but some guys want to use the factory PCM, wiring etc. For a manual system:

The following conditions must be met in order for the A/C compressor clutch to turn on:
Ambient air temperature above 4°C (40°F)
A/C low pressure switch signal circuit is grounded
A/C refrigerant pressure sensor parameter is less than 2957 kPa (429 psi)
PCM receives an A/C request from the HVAC control module
Engine coolant temperature (ECT) is less than 121°C (250°F)
The engine RPM is more than 550 RPM
The throttle position is less than 100%
The HVAC control module monitors the A/C low pressure switch signal circuit. If the voltage signal on this circuit has no voltage drop the module will interpret this condition as a low pressure, disabling the A/C request. The A/C low pressure switch will open its internal contacts at 151 kPa (22 psi) . Then close the contacts at 275 kPa (40 psi) to resume A/C operation. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level.

The PCM monitors the A/C refrigerant pressure sensor signal circuit. The voltage signal on this circuit is proportional to the refrigerant pressure inside the A/C high side pressure line. As the pressure inside the line increases, so does the voltage signal. If the pressure is above 2957 kPa (429 psi) , the A/C compressor output is disabled. When the pressure lowers to 1578 kPa (229 psi) , the PCM enables the compressor to operate.

The sensor information is used by the PCM to determine the following:
The A/C high side pressure
An A/C system load on the engine
An excessive A/C high side pressure
The heat load at the A/C condenser
Once engaged, the compressor clutch will be disengaged for the following conditions:
Ambient air temperature is less than 4°C (40°F)
Throttle position is 100%
The A/C low pressure switch is open
A/C high side pressure is more than 2957 kPa (429 psi)
A/C low side pressure is less than 151 kPa (22 psi)
Engine coolant temperature (ECT) is more than 121°C (250°F)
Engine speed is more than 5500 RPM
Transmission shift
PCM detects excessive torque load
PCM detects insufficient idle quality
PCM detects a hard launch condition